Mechanical elastic structure glasses without metal spring cores and without metal screws

Abstract

Mechanical elastic structure glasses without metal spring cores and without metal screws. The glasses include a frame (1, Fig. 9B), a temple (2, Fig. 9B) and a fixed rotating shaft 3. The two ends of

Description

FIELD OF THE INVENTION The present invention relates to the technical field of eyeglasses having an elastic structure, in particular to a mechanical elastic structure glasses without metal spring cores and without metal screws. BACKGROUND OF THE INVENTION Eyeglasses - also referred to hereafter by the common term “glasses” - typically have two parts, lenses and frames, and are used to improve vision, protect the eyes, and / or for decorative purposes. Glasses can correct myopia, hyperopia, astigmatism, presbyopia, strabismus, amblyopia and many other vision problems. Glasses are divided into near-sighted glasses, far-sighted glasses, presbyopic glasses, astigmatism glasses, plain glasses, computer goggles, swimming goggles, night vision goggles, gaming goggles, wind goggles, sunglasses, toy glasses, etc. There are also special glasses for viewing 3D stereoscopic images or virtual real images. Glasses provide a variety of protection for the eyes. Modem glasses usually have nose pads in the middle of the lens and soft cushions in the left and right arms where they rest on the ears. The entire structure of injection molded glasses are plastic, only the hinge joint of the frame and the temple is made of metal. Currently, there are only two types of hinge structures for all injection molded glasses. One is composed of metal spring cores and metal screws. The metal spring cores and metal screws in this structure are essential components, but the screws have the disadvantage of falling off easily and the metal parts have the risk of causing skin allergy. The other is the structure consisting of only plastic teeth without screws. The structure with only plastic teeth and no screws has no metal parts and loses the elastic function of the spring cores. Therefore, it is a problem in the art to design a kind of glasses that can avoid the problem of metal accessories causing skin allergy and also have the elastic function of spring cores. The beneficial effect of the invention is that it does not contain metal springs or metal screws, that is, it does not contain any metal accessories, and the hinge elastic function is achieved through the injection molding process; it is safe and secure for consumers with metal allergic skin to wear. SUMMARY OF THE INVENTION From the foregoing, it is seen that it is a problem in the art to provide a device meeting the above requirements. According to the present invention, a device is provided which meets the aforementioned requirements and needs in the prior art. The main purpose of this utility model is to overcome the deficiencies in the prior art and provide a mechanical elastic structure glasses without metal spring cores and without metal screws. The glasses can not only realize the elastic function of metal spring, but also avoid the risk that human skin will be allergic to metal accessories. At the same time, it also solves the problem that the metal screw is easy to fall off. The present invention includes: a mechanical elastic structure glasses without metal spring cores and without metal screws, including a frame, a pair of temples, and two fixed rotating shafts. The frame has two ends, each of the two ends having a first tooth and a second tooth, wherein the first tooth having a hole for receiving the respective fixed rotating shaft, and the second tooth has a hole for receiving the respective fixed rotating shaft. Each of the pair of temples has three teeth which are adapted to receive the first tooth of the frame and the second tooth of the frame. The three teeth of the pair of temples are disposed at a front end of the pair of temples and are provided with respective rotation holes in a vertical direction consistent with that of the two fixed rotating shafts. In order to realize the above objectives, the technical scheme adopted by the invention is a device without metal spring and without metal screw, which is injected by plastic material and designed by structure, so as to realize the performance of glasses hinge with metal spring. It is composed of two teeth on the frame, three teeth at the front end of the pair of temples, and two square chamfered fixed rotating shafts . The first tooth and the second tooth of each respective end of the frame fit the three teeth of each respective front end of the respective temple, and each respective fixed rotating shaft runs through the respective first tooth and second tooth and respective three teeth. Preferably, the first tooth and the second tooth of the frame fit with the three teeth of the front end of the pair of temples, and the first tooth and the second tooth of the frame are arranged with a fixed hole in the vertical direction coinciding with the respective fixed rotating shaft, and the fixed holes are used to connect the respective fixed rotating shaft. Preferably, the three teeth of the front end of the pair of temples fit with the first tooth and second tooth of the frame. The three teeth of the front end of the temple are arranged with a rotation hole in the vertical direction consistent with the respective fixed rotating shaft, and the rotation hole is used to connect the respective fixed rotating shaft. The three teeth of the pair of temples include an upper tooth, a middle tooth, and a lower tooth. Preferably, the upper tooth and the lower tooth of the three teeth of the pair of temples have respective openings (gaps) at a front end of the respective rotation holes, and The respective gaps are in communication with the respective rotation holes. The upper and lower teeth of the three teeth of the pair of temples have respective elastic holes and respective channels at a rear end of the respective rotation holes, and the respective channels are in communication with both the respective elastic holes and the respective rotation holes. The respective gaps in the upper and lower teeth of the pair of temples, together with the respective elastic holes and the respective channels of the pair of temples, enable resilient flexing of the upper and lower teeth of the pair of temples, so as to enable rotational movement of the pair of temples relative to the frame. The opening of rotation holes of the upper and lower teeth at the front end of the temple and the elastic structure hole of rotation holes at the rear end of the temple are to realize the elastic function of the temple during the opening and closing process. The front end of the middle tooth of the three teeth of the temple is not open, and the entire circle surrounds the fixed rotating shaft, thereby enabling the stable connection of the frame and the temple under the fixed action of the fixed rotating shaft. Preferably, the two ends of the fixed rotating shaft are set to be square, and the four comers are set with chamfering comers, to ensure that the corresponding position of the fixed rotating shaft and the first tooth and second tooth of the frame are precisely not loosened, and the middle part of the fixed rotating shaft is set to be cylindrical. The middle tooth of the three teeth at the front end of the temple is set with a groove corresponding to the middle part of the fixed rotating shaft. The groove is cylindrical to ensure that the leg is smooth and not stuck during rotation. Compared with the prior art, the beneficial effect of the utility model is: the mechanical elastic structure glasses without metal spring movement and metal screws, that is, without any metal 6 accessories, through the plastic mechanical structure to achieve the hinge elastic function. Consumers with metal allergic skin can be safely and safely worn. It can realize the existing metal spring elastic function, while avoiding the risk of metal accessories being allergic to human skin, and avoiding the problem of metal screw falling off. Moreover, the structure is simple and improves the production efficiency. The following technical points are significant to the present invention are: Square chamfered fixed rotating shaft design; Special-shaped design of three teeth at the front end of the pair of temples; the front end of the middle tooth of the three teeth of the temple is closed without an opening; wherein the upper and lower teeth of the three teeth of the pair of temples have respective gaps at a front end of the respective rotation holes, and the respective gaps are in communication with the respective rotation holes; wherein the upper and lower teeth of the three teeth of the pair of temples have respective elastic holes and respective channels at a rear end of the respective rotation holes, and the respective channels are in communication with both the respective elastic holes and the respective rotation holes; rotation holes; wherein the respective gaps in the upper and lower teeth of the pair of temples, together with the respective elastic holes and the respective channels of the pair of temples, enable resilient flexing of the upper and lower teeth of the pair of temples, so as to enable rotational movement of the pair of temples relative to the frame. Other objectives and advantages of the present invention will be more readily apparent from the following detailed description when read in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a front left perspective view of a Mechanical Elastic Structure Glasses,; FIG. 2 is a rear right perspective view of the Mechanical Elastic Structure Glasses in FIG. 1. FIG. 3 is a rear right perspective view of the Mechanical Elastic Structure Glasses in FIG. 1. FIG. 4 is a front elevational view of the Mechanical Elastic Structure Glasses in FIG. 1. FIG. 5 is a rear elevational view of the Mechanical Elastic Structure Glasses in FIG. 1. FIG. 6 is a left elevational view of the Mechanical Elastic Structure Glasses in FIG. 1, the right view being a mirror image of this view. FIG. 7 is a top plan view of the Mechanical Elastic Structure Glasses in FIG. 1. FIG. 8 is a bottom elevational view of the Mechanical Elastic Structure Glasses in FIG. 1. FIG. 9A is a front left perspective view from above of the assembly of a pin forming part of a left hinge, in a region within a dashed outline; the right hinge being a mirror image thereof. FIG. 9B is an enlarged view of the portion shown in dashed outline in FIG. 9A. FIG. 10A is a rear right perspective view from above of the assembly of the pin forming part of the left hinge, in a region within a dashed outline. FIG. 10B is an enlarged view of the portion shown in dashed outline in FIG. 10A. FIG. 11A is a top plan view of the Mechanical Elastic Structure Glasses in FIG. 7, having a region shown in dashed outline. FIG. 1 IB is an enlarged view of the portion shown in dashed outline in FIG. 11 A. FIG. 1 IC is an enlarged view of the portion shown in dashed outline in FIG. 11 A, showing a second position of a temple member in dashed outline. FIG. 1 ID is an enlarged view of the portion shown in dashed outline in FIG. HA, showing a third position of a temple member in dashed outline. FIG. 12A is an exploded view of the Glasses in FIG. 1, with a dashed circle surrounding a hinge portion. FIG. 12B is an exploded view of the Glasses in FIG. 12A, showing the hinge portion within the dashed circle in FIG. 12A surrounding a hinge portion. DETAILED DESCRIPTION OF THE INVENTION FIG. 1 is a front left perspective view of a Mechanical Elastic Structure Glasses 100. The glasses 100 include a frame 1 and a pair of temples 2. FIG. 2 is a rear right perspective view of the Mechanical Elastic Structure Glasses 100 in FIG. 1. FIG. 3 is a rear right perspective view of the Mechanical Elastic Structure Glasses 100 in FIG. 1. FIG. 4 is a front elevational view of the Mechanical Elastic Structure Glasses in FIG. 1. FIG. 5 is a rear elevational view of the Mechanical Elastic Structure Glasses 100 in FIG. 1. FIG. 6 is a left elevational view of the Mechanical Elastic Structure Glasses 100 in FIG. 1, the right view being a mirror image of this view. FIG. 7 is a top plan view of the Mechanical Elastic Structure Glasses 100 in FIG. 1. FIG. 8 is a bottom elevational view of the Mechanical Elastic Structure Glasses 100 in FIG. 1. FIG. 9A is a front left perspective view of the glasses 100. This is an assembly view shows a fixed rotating shaft 3 forming part of a left hinge, in a region within a dashed outline; the right hinge being a mirror image thereof. The terms left and right are from the viewpoint of a wearer of the glasses 100. FIG. 9B is an enlarged view of the portion shown in dashed outline in FIG. 9A. A hinge structure is shown between the respective temple 2 and the frame 1. The frame 1 includes a pair of teeth, i.e., a first tooth 101a and a second tooth 101b, extending outward from the frame 1, and engaging with the three teeth of the pair of temples 2 (shown in greater detail in FIG. 10B and FIG. 12B. The first tooth 101a has a circular opening therethrough to receive the fixed rotating shaft 3, and the second tooth 101b likewise has a circular opening therethrough to receive the fixed rotating shaft 3. The fixed rotating shaft 3 thereby secures the hinge joint. The fixed rotating shaft 3 has an upper portion 3 a having a cross section in the form of a square chamfered shape, a cylindrical central portion 3b having a circular cross section, and a lower portion 3c having a cross section in the form of a square chamfered shape. The fixed rotating shaft 3 is composed of a resiliently deformable material such as a resiliently deformable plastic material. Any plastic materials can be used which would be known to any one having skill in the hinge arts or plastic material arts. Materials can also include those formed from resiliently deformable rubber as well as from silicone, in addition to plastic. FIG. 10A is a rear right perspective view from above of the assembly of the fixed rotating shaft 3 forming part of the left hinge together with a temple portion in a region within a dashed outline. FIG. 10B is an enlarged view of the portion shown in dashed outline in FIG. 10A, and shows the temple portion which receives the fixed rotating shaft 3 and engages with a glasses portion which likewise receives the fixed rotating shaft 3. The hinge portion of FIG. 10B includes the pair of teeth, i.e. first tooth 101a and second tooth 101b, of FIG. 9B (and also shown in FIG. 12B) which extend from the frame 1; the fixed rotating shaft 3; and three teeth 211,212, and 213 of the pair of temples 2. The tooth 213 is an upper tooth, the tooth 212 is a middle tooth, and the tooth 211 is a lower tooth. These three teeth 211, 212, and 213 engage with the first tooth 101a and the second tooth 101b as shown in FIG. 9B and FIG. 12B. As shown in FIG. 10B, the hinge portion of the pair of temples 2 includes a widened portion 201. The widened portion is shown in greater detail in FIG. 1 IB, and having a first side 53, a second side 53, and an end portion 52. The end portion 52 has a gap 4, as shown in FIG. 10B and in FIG. 1 IB. There is rotation hole 6 in the upper tooth 213, and there is the gap 4 at the end of the temple 2 which is in communication with the rotation hole 6. There is an elastic hole 5 and a channel 51 (shown in FIG. 1 IB). The channel 51 is in communication with both the elastic hole 5 and the rotation hole 6. The lower tooth 211 has a square chamfered hole receiving the fixed rotating shaft 3; the middle tooth 212 has a circular opening receiving the fixed rotating shaft 3; and the upper tooth 213 has a square chamfered hole receiving the fixed rotating shaft 3 (shown in FIG. 12B). The three teeth 211,212, and 213 of the pair of temples 2, together with the first tooth 101a and the second tooth 101b of the frame 1, and together with the fixed rotating shafts 3, form a hinge assembly. There is no gap in the middle tooth 212, so that once the fixed rotating shafts 3 has been inserted into the hinge assembly, the pair of temples 2 cannot be removed from the frame 1, and can only rotate about the fixed rotating shaft 3 as explained further below. The gap 4 in the upper tooth 213, together with the elastic hole 5 and the channel 51, enables resilient flexing of the upper tooth 213 so as to enable rotational movement of the pair of temples 2 relative to the frame 1. The fixed rotating shaft 3 is held against rotation by the first tooth 101a and the second tooth 101b of the frame 1, so that a torque applied by manual engagement of the pair of temples 2 can cause rotational movement of the pair of temples 2 about the fixed rotating shafts 3, because the force applied by the user to the pair of temples 2 is sufficient to resiliently deform the middle tooth 212 so that the gap opens slightly and the rotation hole 6 expands slightly so that the pair of temples 2 can rotate about the fixed rotating shafts 3. The movement is shown in FIG. 1 IC and in FIG. 1 ID. The above discussion of the upper tooth 213 likewise applies to the lower tooth 211, the tooth 211 being essentially identical to the upper tooth 213, and allows rotation of the pair of temples 2 as described above. As described above, and as shown in FIG. 12A and FIG. 12B, the tooth 212 has a circular opening but no gap, and therefore cannot expand to release the fixed rotating shafts 3. Therefore, the middle tooth 212 secures the pair of temples 2 to the frame 1, even when force is applied to the pair of temples 2 to rotatably move it relative to the frame 1. FIG. 11A is a top plan view of the Mechanical Elastic Structure Glasses 100 in FIG. 7, having a region 200 shown in dashed outline. FIG. 1 IB is an enlarged view of the portion 200 shown in dashed outline in FIG. HA. This view shows the top view of the rotation hole 6, the fixed rotating shaft 3, the gap 4, the hole 14 elastic 5, the channel 51, and the side 54, the side 53, and the end portion 52 having the gap 4. The end portion 52 is rounded, so as to permit rotation of the pair of temples 2 aroundt the fixed rotating shafts 3, relative to the frame 1. FIG. 1 IC is an enlarged view of the portion 200 shown in dashed outline in FIG. 11A, showing a second position 300 of a temple 2 in dashed outline. The second position 300 of the temple 2 is reached through an outward movement of the temple 2 pivoting about the fixed rotating shaft 3. The rotation hole 5 is also indicated in dashed outline in this view. The end portion 52 is also shown in dashed outline in the second position 300. In the second position 300, the fixed rotating shaft 3 remains in its original position. FIG. 1 ID is an enlarged view of the portion 200 shown in dashed outline in FIG. 11A, showing a third position 400 of the temple 2 in dashed outline. In this view, the third position 400 of the temple 2 is reached through an inward movement of the temple 2 pivoting about the fixed rotating shaft 3. The rotation hole 5 is also indicated in dashed outline in this view. The end portion 52 is also shown in dashed outline in the second position 300. In the third position 400, the fixed rotating shaft 3 remains in its original position. Due to the square shape of the pin 3, the temple naturally is biased to one of the positions shown, i.e. namely (a) the original position shown in solid lines in FIG. 1 ID, the second position 300 of FIG. 1 IC, or the third position 400 of FIG. HD. The original position of the temple 2 is shown in solid lines in FIG. 1 ID, and is considered the first position of the temple 2. In all, the temple 2 can range in motion by 180 degrees, in 90 degrees increments. FIG. 12A is an exploded view of the Glasses of FIG. 1, with a dashed circle surrounding a hinge portion. In this view, respective holes 61 are shown in the first teeth 101a on opposed sides of the frame 1, the first teeth 101a being shown in detail in FIG. 9B and in FIG. 12B. The holes 6 are respectively shown in the upper teeth 213 (shown in detail in FIG. 10B and FIG. 12B). FIG. 12B is an exploded view of the Glasses of FIG. 12 A, showing the hinge portion within the dashed circle of FIG. 12 A. The first tooth 101a and the second tooth 101b of the frame 1 are shown having respective holes 6land 62. The holes 61 and 62 are square and have no gap or other openings, so that they hold the fixed rotating shafts 3 without permitting rotation of the fixed rotating shafts 3 relative to the frame 1. FIG. 12B shows the three teeth 211, 212, and 213 of the temple 2. The rotation holes 6 are in the lower teeth 211 and the upper 213, and are respectively shaped as chamfered squares with respective gaps 4 (one gap 4 is shown in detail in FIG. 1 IB). A round hole 64 is shown in FIG. 12B, having no gap or other opening, and is described above. The round hole 64 retains the fixed rotating shafts 3 so that the pair of temples 2 is secured for pivotable movement relative to the frame 1. In the preferred embodiment, the three teeth 211,212, and 213 receive the first tooth 101a and the second tooth 101b in snug engagement so that there the pair of temples 2 can rotate only in a single plane of motion. The fit is tight enough to prevent motion of the pair of temples 2 relative to the frame 1, at all times other than when force is being applied to move the pair of temples 2 to the second position or the third position described hereinabove. When a torque is applied to the pair of temples 2, the rotation of the rotation hole 6 about the fixed rotating shaft 3 results in a force urging the gap 4 to open, and this is possible due to the presence of the elastic hole 5 and channel 51, allowing rotation the hole 6 to be deformed slightly to accommodate rotation of the fixed rotating shaft3 therein. The following technical points are significant to the present invention are: a square chamfered fixed rotating shaft design (the fixed rotating shaft 3 and the rotation hole 6); a special-shaped design of three teeth (211,212, and 213) at the front end of the pair of temples, wherein the front end of the middle tooth 212 of the three teeth of the pair of temples 2 is closed without a gap or opening at the end thereof (such that the hole 64 cannot expand and thereby retains the fixed rotating shaft 3 securely), and wherein the front end of the upper tooth 213 and lower tooth 211 of the three teeth of the pair of temples 2 have gaps 4 which are openings; and there are elastic structure designs at the rear end of the openings of the upper and lower teeth of the three teeth of the temple (namely the respective elastic holes 5 and respective channels 51). In order to realize the above objectives, the technical scheme adopted by the invention is a device without metal spring and without metal screw, which is formed by injection molding of plastic material and designed by structure, so as to realize the equivalent performance of a glasses hinge with a metal spring device. It is composed of two teeth on the frame, three teeth at the front end of the temple, and a square chamfered fixed rotating shaft through the respective teeth. In the foregoing, all indicated orientations or positional relationships are only intended to facilitate the description and simplification of the invention, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, be constructed, and operate in a specific orientation, and therefore cannot be understood as a limitation of the invention. In addition, the terms "first", "second", "third", and the like are only used to distinguish descriptions and cannot be understood as indicative or indicative of relative importance. Further, the two teeth 101 of the frame 1 fit with the front three teeth 201 of the pair of temples 2. The twoteeth 101 of the frame 1 are provided with fixing holes in the vertical direction that coincide with the fixed rotating shaft 3, and the fixing holes are used to connect a portion of both ends of the fixed rotating shaft 3. The three teeth 201 at the front end of the pair of temples 2 fit into the two teeth 101 of the frame 1. The three teeth 201 at the front end of the pair of temples 2 are provided with a rotation hole 6 in a vertical direction that coincides with the fixed rotating shaft 3. The rotation hole 6 is used to connect the other part of both ends of the fixed rotating shaft 3. Further, the two ends of the fixed rotating shaft 3 are arranged in a square shape, and the four comers thereof are provided with chamfers to ensure that the corresponding positions of the fixed rotating shaft 3 and the two teeth 101 of the frame 1 are precisely matched and not loose. The middle section of the fixed rotating shaft 3 is arranged in a cylindrical shape. The middle teeth 212 of the three teeth 201 on the front end of the pair of temples 2 are provided with grooves in a cylindrical shape corresponding to the middle section of the fixed rotating shafts 3 to ensure that the pair of temples 2 is smooth and does not get stuck during rotation. At the same time, the cylindrical shaped grooves can facilitate the clamping of the fixed rotating shafts 3. Further, one end of the upper and lower tooth rotation holes 6 of the front three teeth 201 of the pair of temples 2 is provided with an opening 4, and the other end of the rotation hole 6 is provided with an elastic hole 5. The openings 4 at the front end of the upper tooth 213 and the lower tooth 211 of the pair of temples 2, the rotation holes 6 and the elastic holes 5 at the rear end of the pair of temples 2, rotation hole 6 are both used to achieve the elastic function of the pair of temples 2 during the opening and closing process; the front end of the three teeth 201 on the front end of the pair of temples 2 is not open, and the entire circle surrounds the fixed rotating shaft 3 to ensure stable connection between the fixed frame 1 and the pair of temples 2 under the fixed action of the fixed rotating shafts 3. The working principle and specific use process of the mechanical elastic structure glasses without metal spring movement and metal screws: during the rotation process of the pair of temples 2, the difference between the diagonal distance of the square fixed rotating shafts 3 and the square distance of the square fixed rotating shafts 3, as well as the material elasticity of the plastic temples 2, are utilized to achieve the elastic function of the temples 2 during the opening and closing process. Based on the above principles, the glasses can be opened in the following two ways: First, the temple can be fully opened to 180 °, requiring external force to close it; Secondly, the temple can be opened 90 + 45 ° to naturally return to the vertical position with the frame. In another embodiment, the fixed rotating shafts 3 can be formed in two parts, so that one of the ends can be removed for ease of insertion into one side of the rotation hole 6, and then reassembled by introduction of the removed end into an opposite side of the rotation hole 6. The invention being thus described, it will be evident that the same may be varied in many ways by a routineer in the applicable arts. Such variations are not to be regarded as a departure from the spirit and scope of the invention and all such modifications are intended to be included within the scope of the claims. Claim:

Claims

1. Mechanical elastic structure glasses without metal spring cores and without metal screws, comprising:a frame,a pair of temples, andtwo fixed rotating shafts for connecting said frame to said pair of temples, wherein the two fixed rotating shafts are composed of a resiliently deformable material;said frame having two ends, each of the two ends having a first tooth and a second tooth, said first tooth having a hole for receiving said respective fixed rotating shaft; said second tooth of said frame having a hole for receiving said respective fixed rotating shaft; andeach of said pair of temples having three teeth which are adapted to receive said first tooth of said frame and said second tooth of said frame;wherein said first tooth and said second tooth of the two end of said frame have respective fixed holes aligned in a vertical direction consistent with that of said pair of temples;wherein said three teeth of said pair of temples are disposed at a front end of said pair of temples and are provided with respective rotation holes in a vertical direction consistent with that of said two fixed rotating shafts;wherein the upper and lower teeth of the three teeth of the pair of temples have respective gaps at a front end of the respective rotation holes, and the respective gaps are in communication with the respective rotation holes;wherein the upper and lower teeth of the three teeth of the pair of temples have respective elastic holes and respective channels at a rear end of the respective rotation holes, and the respective channels are in communication with both the respective elastic holes and the respective rotation holes;5 wherein the respective gaps in the upper and lower teeth of the pair of temples, together with the respective elastic holes and the respective channels of the pair of temples, form an elastic structure and enable resilient flexing of the upper and lower teeth of the pair of temples, so as to enable rotational movement of the pair of temples relative to the frame;wherein the two ends of the two respective fixed rotating shafts are square, and the four10 comers of the two square ends are provided with chamfers; and where a middle section of said two respective fixed rotating shafts is set as a cylinder;wherein the middle tooth of said three teeth of said pair of temples is provided with a bore corresponding to the middle section of the two respective rotating shafts, and wherein said bore is cylindrical.

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