An inside diameter measuring device and method of use

Abstract

The present application relates to the technical field of measuring equipment, and discloses an inner diameter measuring device and a method thereof. The inner diameter measuring device comprises a mounting shell, an adjustable contact, a movable contact, a display and a protective bridge. The adjustable contact is movably arranged in the mounting shell along an axial direction. One end of the adjustable contact is provided with an adjustable contact point, and the other end of the adjustable contact is connected with one of a scale bar or a reader. The movable contact is elastically arranged in the mounting shell along the axial direction. One end of the movable contact is provided with a movable contact point, and the other end of the movable contact is connected with the other one of the scale bar or the reader. The protective bridge is elastically arranged outside the mounting shell along the axial direction. When measuring the inner diameter of different specifications of inner holes, the adjustable contact point and two positioning contact points can form three-point positioning, so that the inner diameter to be measured can be quickly and accurately found, the time required for measurement is reduced, and the standard inner diameter ring is not needed to be found to set the basic zero position, thereby avoiding continuous setting and correction and reducing the measurement difficulty.

Description

Technical Field

[0001] This invention relates to the field of measuring equipment technology, and in particular to an internal diameter measuring device and its usage method. Background Technology

[0002] Length measuring instruments are tools used to measure length. Their basic principle is to obtain a measurement result by comparing the length to be measured with a known length. These tools have wide applications in science, technology, engineering, and daily life. When machining internal holes, it is often necessary to measure the inner hole diameter to determine whether the machined dimensions meet the drawing requirements.

[0003] Currently, internal diameter gauges are generally used to measure internal diameters. However, existing technology has a limited measurement range; it can only measure diameters with small deviations from the set value. Furthermore, when used for internal diameter measurement, it must be calibrated before each use, requiring the search for a standard internal diameter ring gauge close to the target size to set the baseline zero point. During measurement, it can only show how much larger or smaller the value is than zero. Therefore, when dealing with internal diameters of different specifications, continuous setting and calibration are necessary before use, leading to measurement difficulties. Summary of the Invention

[0004] The purpose of this invention is to provide an inner diameter measuring device and its usage method to solve the problem that the measurement range of the inner diameter gauge in the prior art is limited, and it can only measure the diameter of the hole with a small deviation from the set value. Moreover, during the measurement, it can only see how much larger or smaller than zero. Therefore, when facing inner holes of different specifications, it is necessary to continuously set and calibrate before it can be used, which makes the measurement difficult.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] On one hand, the present invention provides an inner diameter measuring device, comprising:

[0007] The mounting housing has a movable opening on one side along the axial direction;

[0008] An adjustable contact is movably disposed within the mounting housing along the axial direction; one end of the adjustable contact has an adjustable contact point, which extends to the outside through the movable opening; the other end of the adjustable contact is connected to either a scale strip or a reader; the length of the adjustable contact along the axial direction is adjustable.

[0009] A movable contact is elastically disposed within the mounting housing along the axial direction; one end of the movable contact has a movable contact point that can extend through the mounting housing to the outside; the other end of the movable contact is connected to either the reader or the scale bar, the reader being used to read the scale bar; the adjustable contact and the movable contact are located on opposite sides of the mounting housing along the axial direction.

[0010] A protective bridge is elastically disposed outside the mounting housing along the axial direction; at least two positioning contacts are provided at the end of the protective bridge away from the adjustable contact, and the lines connecting the at least two positioning contacts and the adjustable contact can form an isosceles triangle;

[0011] A display, communicatively connected to the reader, is used to display the spacing between the adjustable contact and the movable contact.

[0012] As an alternative to the aforementioned inner diameter measuring device, the adjustable contact includes a movable base and a connector. Part of the movable base is movably disposed inside the mounting housing, while another part of the movable base is located outside the mounting housing. The connector is detachably connected to the end of the movable base away from the moving contact.

[0013] As an alternative to the aforementioned inner diameter measuring device, the adjustable contact further includes a connecting rod, the two opposite ends of which are detachably connected to the movable seat and the connector, respectively; the connecting rod extends along the axial direction.

[0014] As an alternative to the aforementioned inner diameter measuring device, the adjustable contact further includes a locking member that can pass through the mounting housing radially and press against the movable seat.

[0015] As an optional embodiment of the aforementioned inner diameter measuring device, the inner diameter measuring device further includes a first elastic element, and the inner wall of the mounting housing is provided with a first limiting step. The opposite ends of the first elastic element abut against the first limiting step and the moving contact, respectively, so that the moving contact always has a tendency to move away from the adjustable contact.

[0016] As an optional embodiment of the aforementioned inner diameter measuring device, the inner diameter measuring device further includes a second elastic element. The outer wall of the mounting housing is provided with a second limiting step. The opposite ends of the second elastic element abut against the second limiting step and the protective bridge, respectively, so that the protective bridge always has a tendency to move away from the adjustable contact.

[0017] As an alternative to the aforementioned inner diameter measuring device, the mounting housing includes a main housing and a cover housing. The main housing has a movable opening and a mounting opening at both ends along the axial direction, respectively. The cover housing is detachably connected to the mounting opening, and the movable contact can extend through the cover housing to the outside.

[0018] As an alternative to the aforementioned inner diameter measuring device, a handle rod is vertically mounted on the mounting housing.

[0019] As an alternative to the aforementioned inner diameter measuring device, the display may be located in the mounting housing, in the handle, or separately.

[0020] On the other hand, the present invention provides a method of using an inner diameter measuring device, which is performed using the inner diameter measuring device as described above. The method of using the inner diameter measuring device includes the following steps:

[0021] The position of the adjustable contact on the mounting housing is adjusted by moving the adjustable contact, and the length of the adjustable contact is adjusted so that the distance between the adjustable contact and the moving contact is greater than the inner diameter of the inner hole to be measured.

[0022] The adjustable contact of the adjustable contact is abutted against the inner wall of one side of the inner hole to be tested, and at least two of the positioning contacts of the bridge are abutted against the inner wall of the other side of the inner hole to be tested.

[0023] While maintaining continuous contact between the adjustable contact and at least two positioning contacts and the inner wall of the inner hole to be measured, so that the cross section of the inner hole to be measured along the axial direction always includes the line segment formed by the connection of the adjustable contact and the moving contact, the moving contact of the moving contact is then moved along the axial direction of the inner hole to be measured, and the minimum value of the measurement is selected through the display.

[0024] The beneficial effects of this invention are as follows:

[0025] The internal diameter measuring device includes a mounting housing, an adjustable contact, a moving contact, a display, and a bridge. The mounting housing has a movable opening on one axial side. The adjustable contact is axially movable within the mounting housing. One end of the adjustable contact has an adjustable contact point that extends to the outside through the movable opening. The other end of the adjustable contact is connected to either a scale bar or a reader. Thus, by adjusting the position of the adjustable contact on the mounting housing, the initial positions of the adjustable contact point and the scale bar or reader can be adjusted.

[0026] The moving contact is elastically mounted axially within the mounting housing. One end of the moving contact has a movable contact point that extends through the housing to the outside. The other end of the moving contact is connected to either a reader or a scale strip. The reader is used to read the scale strip. The adjustable contact and the moving contact are located on opposite sides of the mounting housing axially. When measuring the inner diameter of the hole to be measured, the relative position of the reader and the scale strip can be adjusted by the contact between the adjustable contact and the moving contact on the hole wall. This allows for direct measurement of the distance between the adjustable contact and the moving contact, thus determining the diameter of the hole. This process, through the elastic movement of the moving contact, allows for automatic axial extension and retraction, thereby automatically adjusting the distance between the adjustable contact and the moving contact. A display is connected to the reader to show the distance between the adjustable contact and the moving contact. Therefore, when measuring the inner diameter of holes of different specifications, it is unnecessary to find a standard inner diameter ring gauge to set the baseline zero point, thus avoiding continuous setting and correction and reducing the measurement difficulty.

[0027] The protective bridge is axially elastically set outside the mounting housing. At least two positioning contacts are provided at the end of the protective bridge away from the adjustable contact. The line connecting the at least two positioning contacts and the adjustable contact can form an isosceles triangle, so that the adjustable contact and the two positioning contacts can form a three-point positioning, which facilitates quick and accurate location of the inner diameter to be measured and reduces the measurement time.

[0028] Meanwhile, the length of the adjustable contact along the axial direction can be adjusted, and the adjustable contact is movable along the axial direction within the mounting housing. Thus, by adjusting the position of the adjustable contact on the mounting housing and the length of the adjustable contact itself, the measurement of the inner diameter of large or small holes can be achieved.

[0029] The method of using the inner diameter measuring device of the present invention is accomplished using the inner diameter measuring device as described above. The method of using this inner diameter measuring device is simple and convenient, accurate, and has a wide range of adaptability, making it easy for on-site personnel to accept. By adjusting the position of the adjustable contact on the mounting housing and adjusting the length of the adjustable contact itself, it can meet the measurement of inner holes of different specifications. The adjustable contact and two positioning contacts can form a three-point positioning, which facilitates quick and accurate location of the inner diameter to be measured, reducing the measurement time required. Moreover, the display directly shows the measured value during measurement, eliminating the need to find a standard inner diameter ring gauge to set the basic zero position, thereby avoiding continuous setting and correction and reducing the measurement difficulty. Attached Figure Description

[0030] Figure 1 This is a cross-sectional view of the inner diameter measuring device provided in an embodiment of the present invention;

[0031] Figure 2 This is a cross-sectional view of another inner diameter measuring device provided in an embodiment of the present invention;

[0032] Figure 3 This is a top view of the inner diameter measuring device provided in an embodiment of the present invention;

[0033] Figure 4 This is a flowchart illustrating the method of using the inner diameter measuring device provided in an embodiment of the present invention.

[0034] In the picture:

[0035] 1. Housing; 11. Movable opening; 12. First limiting step; 13. Second limiting step; 14. Main housing; 141. Installation opening; 15. Cover; 16. Handle rod; 2. Adjustable contact; 21. Adjustable contact point; 22. Scale strip; 23. Movable base; 24. Connector; 25. Connecting rod; 26. Locking element; 3. Moving contact; 31. Moving contact point; 32. Reader; 4. Display; 5. First elastic element; 6. Protective bridge; 61. Positioning contact point; 7. Second elastic element; 8. Inner hole to be measured. Detailed Implementation

[0036] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. The terms "first position" and "second position" refer to two different positions. Furthermore, "above," "on top of," and "over" the first feature in relation to the second feature includes the first feature directly above and diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "under," and "below" the first feature in relation to the second feature includes the first feature directly below and diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0038] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0039] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0040] like Figures 1-3 As shown, this embodiment provides an inner diameter measuring device for measuring the inner diameter of the inner hole 8 to be measured.

[0041] The internal diameter measuring device includes a mounting housing 1, an adjustable contact 2, a moving contact 3, a display 4, and a protective bridge 6. The mounting housing 1 has a movable opening 11 on one side along the axial direction. The adjustable contact 2 is movably disposed within the mounting housing 1 along the axial direction. One end of the adjustable contact 2 has an adjustable contact point 21, which extends to the outside through the movable opening 11. The other end of the adjustable contact 2 is connected to either a scale strip 22 or a reader 32. Thus, by adjusting the position of the adjustable contact 2 on the mounting housing 1, the initial positions of the adjustable contact point 21 and the scale strip 22 or reader 32 can be adjusted.

[0042] The movable contact 3 is elastically disposed within the mounting housing 1 along the axial direction. One end of the movable contact 3 has a movable contact 31, which can extend through the mounting housing 1 to the outside. The other end of the movable contact 3 is connected to either a reader 32 or a scale strip 22. The reader 32 is used to read the scale strip 22. The adjustable contact 21 and the movable contact 31 are located on opposite sides of the mounting housing 1 along the axial direction. Thus, when measuring the inner diameter of the inner hole 8 to be measured, the relative position of the reader 32 and the scale strip 22 can be adjusted by the contact of the adjustable contact 21 and the movable contact 31 against the hole wall of the inner hole 8 to be measured. The distance between the adjustable contact 21 and the movable contact 31 can then be directly measured to determine the diameter of the inner hole 8 to be measured. This process is achieved by the elastic movement of the movable contact 31, which allows the movable contact 31 to automatically extend and retract along the axial direction, thereby realizing the automatic adjustment of the distance between the adjustable contact 21 and the movable contact 31. The display is connected to the reader 32 to show the distance between the adjustable contact 21 and the moving contact 31. Therefore, when measuring the inner diameter of different sizes of inner holes 8, it is not necessary to find a standard inner diameter ring gauge to set the baseline zero position, thus avoiding constant setting and correction and reducing the measurement difficulty. Optionally, the communication connection includes a wired communication connection and a wireless communication connection.

[0043] Among them, the guard bridge 6 is elastically set outside the mounting housing 1 along the axial direction. At least two positioning contacts 61 are provided at the end of the guard bridge 6 away from the adjustable contact 2. The line connecting the at least two positioning contacts 61 and the adjustable contact 21 can form an isosceles triangle, so that the adjustable contact 21 and the two positioning contacts 61 can form a three-point positioning, which facilitates the quick and accurate location of the inner diameter to be measured and reduces the measurement time required.

[0044] Meanwhile, the adjustable contact 2 has an adjustable length along its axial direction and is movably disposed within the mounting housing 1. By adjusting the position of the adjustable contact 2 on the mounting housing 1 and its length, the measurement of the inner diameter of large or small holes can be achieved. Optionally, a handle 16 is vertically disposed on the mounting housing 1, allowing the operator to move the inner diameter measuring device by holding the handle 16 to adjust its position, thus reducing the difficulty of measuring the inner diameter of the inner hole 8. Further, optionally, the display 4 is disposed on the mounting housing 1, on the handle 16, or separately, allowing the inner diameter measuring device to be categorized into different types based on the position of the display 4, thereby meeting different working conditions.

[0045] like Figure 1 and Figure 2As shown, the adjustable contact 2 includes a movable base 23 and a connector 24. Part of the movable base 23 is movably disposed inside the mounting housing 1, while another part of the movable base 23 is located outside the mounting housing 1. The connector 24 is detachably connected to the end of the movable base 23 away from the moving contact 3. Thus, by moving the movable base 23 and changing the connector 24, the measurement range of the inner diameter measuring device can be adjusted. In another embodiment, the adjustable contact 2 also includes a connecting rod 25. The opposite ends of the connecting rod 25 are detachably connected to the movable base 23 and the connector 24, respectively, and the connecting rod 25 extends axially. Thus, by setting the connecting rod 25, the measurement range of the inner diameter measuring device can be further expanded, enabling the inner diameter measuring device to measure inner holes with larger inner diameters, meeting the needs of actual working conditions.

[0046] Furthermore, the adjustable contact 2 also includes a locking member 26, which can pass through the mounting housing 1 radially and press against the movable seat 23, thereby locking the movable seat 23 and preventing displacement of the movable seat 23 during measurement, which could lead to measurement failure. Optionally, the locking member 26 is a locking screw, so that by rotating the locking screw, the locking screw can be moved relative to the mounting housing 1, facilitating the locking of the movable seat 23.

[0047] Furthermore, the inner diameter measuring device also includes a first elastic element 5. The inner wall of the mounting housing 1 is provided with a first limiting step 12. The opposite ends of the first elastic element 5 abut against the first limiting step 12 and the moving contact 3, respectively, to ensure that the moving contact 3 always has a tendency to move away from the adjustable contact 2. Thus, when the moving contact 3 initially abuts against the inner wall of the inner hole 8 to be measured, the moving contact 3 is compressed due to the abutment. After adjusting the positions of the adjustable contact 21 and the moving contact 31 to accurately locate the inner diameter to be measured, the first elastic element 5 can rebound to drive the moving contact 3 out of the mounting housing 1, thereby achieving automatic adjustment of the position of the moving contact 31. Optionally, the first elastic element 5 is a spring.

[0048] The inner diameter measuring device also includes a second elastic element 7. A second limiting step 13 is provided on the outer wall of the mounting housing 1. The opposite ends of the second elastic element 7 abut against the second limiting step 13 and the guard bridge 6, respectively, to ensure that the guard bridge 6 always tends to move away from the adjustable contact 2. Thus, when the positioning contact 61 initially abuts against the inner wall of the inner hole 8 to be measured, the guard bridge 6 is abutted, causing the second elastic element 7 to be compressed. After adjusting the positions of the adjustable contact 21 and the moving contact 31 to accurately locate the inner diameter to be measured, the second elastic element 7 can rebound to drive the guard bridge 6 out of the mounting housing 1, thereby achieving automatic adjustment of the three-point positioning. Optionally, the second elastic element 7 is a spring.

[0049] Furthermore, the mounting housing 1 includes a main housing 14 and a cover 15. The main housing 14 has a movable opening 11 and a mounting opening 141 at both ends along the axial direction. The cover 15 is detachably connected to the mounting opening 141, and the movable contact 31 can extend through the cover 15 to the outside. Thus, the detachable connection between the cover 15 and the main housing 14 facilitates the installation of internal components of the inner diameter measuring device by operators, reducing production difficulty, and also facilitates the disassembly and maintenance of the inner diameter measuring device. Optionally, the cover 15 can abut against the movable contact 3 and the protective bridge 6 along the axial direction to prevent the movable contact 3 and the protective bridge 6 from detaching from the main housing 14.

[0050] This embodiment also provides a method for using the inner diameter measuring device, which is performed using the inner diameter measuring device as described above. Figure 4 As shown, the method of using the described inner diameter measuring device includes the following steps:

[0051] The position of the adjustable contact 2 on the mounting housing 1 is adjusted by moving the adjustable contact 2, and the length of the adjustable contact 2 is adjusted so that the distance between the adjustable contact 21 and the moving contact 31 is greater than the inner diameter of the inner hole 8 to be measured.

[0052] The adjustable contact 21 of the adjustable contact 2 is placed against the inner wall on one side of the inner hole 8 to be tested, and at least two positioning contacts 61 of the guard bridge 6 are placed against the inner wall on the other side of the inner hole 8 to be tested.

[0053] While maintaining continuous contact between the adjustable contact 21 and at least two positioning contacts 61 and the inner wall of the inner hole 8 to be measured, so that the cross section of the inner hole 8 to be measured along the axial direction always includes the line segment formed by the connection of the adjustable contact 21 and the moving contact 31, the moving contact 3 of the moving contact 3 is moved along the axial direction of the inner hole 8 to be measured, and the minimum value of the measurement is selected through the display 4.

[0054] In this embodiment, the method of using the inner diameter measuring device is as described above. The method of using this inner diameter measuring device is simple and convenient, accurate, and has a wide range of adaptability, making it easy for on-site personnel to accept. By adjusting the position of the adjustable contact 2 on the mounting housing 1 and adjusting the length of the adjustable contact 2 itself, it can meet the measurement of inner holes 8 of different specifications. The adjustable contact 21 and the two positioning contacts 61 can form a three-point positioning, which makes it convenient to quickly and accurately find the inner diameter to be measured, reducing the measurement time. Moreover, the display 4 directly displays the measured value during measurement, without the need to find the standard inner diameter ring gauge to set the basic zero position, thereby avoiding continuous setting and correction and reducing the measurement difficulty.

[0055] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. An inside diameter measuring device characterized by, The utility model relates to a kind of adjustable contact and movable contact, including: Mounting shell (1), the mounting shell (1) is opened with mobile opening (11) along the axial one side; Adjustable contact (2), the adjustable contact (2) is movably arranged in the mounting shell (1) along the axial direction;One end of the adjustable contact (2) is provided with adjustable contact point (21), and the adjustable contact point (21) is exposed to the outside world via the mobile opening (11), and the other end of the adjustable contact (2) is connected with one of scale bar (22) or reader (32);The length of the adjustable contact (2) along the axial direction is adjustable; Movable contact (3), the movable contact (3) is elastically arranged in the mounting shell (1) along the axial direction;One end of the movable contact (3) is provided with movable contact point (31), and the movable contact point (31) can be exposed to the outside world from the mounting shell (1), and the other end of the movable contact (3) is connected with the other of the scale bar (22) or the reader (32), and the reader (32) is used to read the scale bar (22);The adjustable contact point (21) and the movable contact point (31) are located on the opposite sides of the mounting shell (1) along the axial direction; Guard bridge (6), the guard bridge (6) is elastically arranged outside the mounting shell (1) along the axial direction;The end of the guard bridge (6) away from the adjustable contact (2) is provided with at least two positioning contact points (61), and the line connecting the at least two positioning contact points (61) and the adjustable contact point (21) can form an isosceles triangle; Display (4), the display (4) is connected with the reader (32) in communication, for showing the distance between the adjustable contact point (21) and the movable contact point (31); First elastic member (5), the inner wall of the mounting shell (1) is provided with first limiting step (12), and the opposite ends of the first elastic member (5) are respectively abutted on the first limiting step (12) and the movable contact (3), so that the movable contact (3) always has the movement trend away from the adjustable contact (2); Second elastic member (7), the outer wall of the mounting shell (1) is provided with second limiting step (13), and the opposite ends of the second elastic member (7) are respectively abutted on the second limiting step (13) and the guard bridge (6), so that the guard bridge (6) always has the movement trend away from the adjustable contact (2).

2. The inside diameter measuring device of claim 1, wherein, The adjustable contact (2) includes moving seat (23) and joint (24), part of the moving seat (23) is movably arranged in the mounting shell (1), and the other part of the moving seat (23) is located outside the mounting shell (1), and the joint (24) is detachably connected to the end of the moving seat (23) away from the movable contact (3).

3. The inside diameter measuring device of claim 2, wherein, The adjustable contact (2) further includes connecting rod (25), and the opposite ends of the connecting rod (25) are respectively detachably connected to the moving seat (23) and the joint (24);The connecting rod (25) is arranged along the axial direction.

4. The inside diameter measuring device of claim 2, wherein, The adjustable contact (2) further comprises a locking member (26) capable of penetrating the mounting shell (1) along the radial direction of the mounting shell (1) and being press-connected to the moving seat (23).

5. The inside diameter measuring device according to any one of claims 1 to 4, characterized in that The mounting shell (1) comprises a main shell (14) and a cover shell (15), the main shell (14) is provided with the moving opening (11) and a mounting opening (141) at two ends along the axial direction respectively, the cover shell (15) is detachably connected to the mounting opening (141), and the movable contact (31) can penetrate the cover shell (15) to the outside.

6. The inside diameter measuring device of any one of claims 1 to 4, wherein A handle rod (16) is vertically arranged on the mounting shell (1).

7. The inside diameter measuring device of claim 6, wherein, The display (4) is arranged on the mounting shell (1), the handle rod (16) or separately arranged.

8. A method of using an inside diameter measuring device, characterized by, The use method of the inner diameter measuring device according to any one of claims 1-7 comprises the following steps: The position of the adjustable contact (2) on the mounting shell (1) is adjusted by moving the adjustable contact (2), and the length of the adjustable contact (2) is adjusted, so that the distance between the adjustable contact (21) and the movable contact (31) is greater than the to-be-measured inner diameter of the to-be-measured inner hole (8); The adjustable contact (21) of the adjustable contact (2) is abutted against the inner wall of one side of the to-be-measured inner hole (8), and at least two positioning contacts (61) of the protective bridge (6) are abutted against the inner wall of the other side of the to-be-measured inner hole (8); Under the condition that the adjustable contact (21) and the at least two positioning contacts (61) are continuously in contact with the inner wall of the to-be-measured inner hole (8), the to-be-measured inner hole (8) always contains a line segment formed by the adjustable contact (21) and the movable contact (31) in the axial direction of the to-be-measured inner hole (8), the movable contact (31) of the movable contact (3) is moved along the axial direction of the to-be-measured inner hole (8), and the minimum value of the measurement is selected by the display (4).

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