Knock type writing instrument

Abstract

To provide a knock type writing instrument capable of preventing uneven wear of a tip by devising a positional relation between a knock mechanism and a refill to facilitate rotation of the refill during a knock operation.SOLUTION: Provided is a knock type writing instrument having a knock mechanism and a refill housed within a cylindrical case, the knock mechanism having a rotor that rotates in response to a knock operation, and an axial center of the rotor being eccentric with respect to an axial center of the refill.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a knock mechanism for a knock-type writing instrument. [Background technology]

[0002] 2. Description of the Related Art Conventionally, knock-type writing implements, such as the knock-type ballpoint pens described in Patent Documents 1 and 2, are known in which a refill is popped out from the front end of a cylindrical case by pressing a knock member at the rear end. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2018-108663 A [Patent Document 2] Registered Utility Model No. 3159535 Summary of the Invention [Problem to be solved by the invention]

[0004] In the knock-type ballpoint pens shown in Patent Documents 1 and 2 above, the rotor abuts against the rear end of the refill, and the axis of the entire knock mechanism including the rotor is arranged concentrically with the axis of the refill. In such a configuration, even if the rotor rotates, the rotation is not easily transmitted to the refill, and rotation of the refill accompanying the knocking action is unlikely to occur. On the other hand, when writing with a writing instrument, some users have a fixed way of holding the writing instrument, and always write with the writing instrument in the same position and in the same posture. In such a usage, for example, in a ballpoint pen, the contact points between the ball and the inner surface of the ball holder that holds the ball are concentrated at specific points in the ballpoint pen tip, causing uneven wear of the inner surface of the ball holder. This problem is not limited to ballpoint pens, but also occurs in refills with tips (bullet tips) that are symmetrical around the axis, such as felt-tip pens, where the tip wears unevenly. If the tip of a writing instrument wears unevenly, it can result in poor writing feel, an inability to write lines of uniform thickness, and even a shortened lifespan (you can no longer write before the ink runs out).

[0005] Therefore, the present invention aims to provide a knock-type writing instrument that has an innovative positional relationship between the knock mechanism and the refill that makes it easier to rotate the refill during the knock action and prevents uneven wear of the tip. [Means for solving the problem]

[0006] In order to solve the above problems, the present invention has the following configuration. A knock-type writing instrument in which a knock mechanism and a refill are housed in a cylindrical case, The knock mechanism has a rotor that rotates in response to a knock action, The axis of the rotor is eccentric with respect to the axis of the refill. A knock-type writing instrument characterized by the above. Effect of the Invention

[0007] In the knock-type writing instrument of the present invention, the axis of the rotor of the knock mechanism is eccentric with respect to the axis of the refill, making it easier to rotate the axis of the refill with the knocking action, and preventing uneven wear of the tip. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a side view of a knock-type ballpoint pen 1 according to an embodiment of the present invention. [Diagram 2] 1 is a cross-sectional view of the rear end side of a knock-type ballpoint pen 1 according to an embodiment of the present invention. [Diagram 3] 3 is a cross-sectional view taken along line AA in FIG. 2, seen from the rear end side. [Figure 4] 1 is a partially cutaway perspective view of the main components of a knock-type ballpoint pen 1 according to an embodiment of the present invention. FIG. [Diagram 5]1 is a diagram of a rotor 42 of a knock-type ballpoint pen 1 according to an embodiment of the present invention. [Figure 6] 2 is a cross-sectional view of a rear case 22 of the knock-type ballpoint pen 1 according to the embodiment of the present invention. FIG. [Figure 7] 1A to 1C are diagrams illustrating the operation of a knock-type ballpoint pen 1 according to an embodiment of the present invention. [Figure 8] FIG. 4 is a diagram of a rotor 42 according to a modified example of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] [Embodiment] Hereinafter, a knock-type ballpoint pen 1, which is an embodiment of a knock-type writing instrument according to the present invention, will be described with reference to the drawings. In the following description, the same reference numerals in different drawings indicate parts having the same functions, and duplicated descriptions in each drawing will be omitted as appropriate. The long axis direction of the knock type ballpoint pen 1 is simply referred to as the "axial direction." The side of the knock type ballpoint pen 1 from which the ballpoint pen refill 3 protrudes is referred to as the front or tip, and the opposite side is referred to as the rear.

[0010] [Overall configuration] FIG. 1 is a side view of a knock-type ballpoint pen 1 according to the present embodiment. The knock-type ballpoint pen 1 of this embodiment has a cylindrical case 2 , a ballpoint pen refill 3 and a knock mechanism 4 housed in the cylindrical case 2 , and a clip 5 provided on the outer circumferential surface of the cylindrical case 2 . The cylindrical case 2 is divided near the center in the longitudinal direction into two members, a front case 21 and a rear case 22. The front case 21 and the rear case 22 are detachably joined by screws. A ballpoint pen refill 3 is housed in the cylindrical case 2 in a replaceable manner, and a knock mechanism 4 is housed in the rear of the ballpoint pen refill 3.

[0011] A knock member 41 protrudes from a rear end opening 221 of the rear case 22, and a knock action is performed when the knock member 41 is pressed down. In addition, a clip 5 is provided on the outer peripheral surface of the rear case 22. By the knocking action, the ball-point pen tip 31 of the ball-point pen refill 3 appears and disappears from the tip opening 211 at the tip of the front case 21. The cylindrical case 2 may be divided into three or more members. As a means for connecting and separating a plurality of members, any other engaging means, fitting means, etc. may be used in addition to screws. In addition, in this embodiment, the cylindrical case 2 is a round cylinder with a circular cross section, but this is not limited to this, and the cross section may be any shape, such as a polygon such as a triangle, a rectangle, or a hexagon, or an ellipse.

[0012] [Knock mechanism] Fig. 2 is a cross-sectional view of the rear end side of the knock type ballpoint pen 1 according to an embodiment of the present invention. Fig. 3 is a cross-sectional view of the line AA in Fig. 2 as viewed from the rear end side. Fig. 4 is a combination of a perspective view of the ballpoint pen refill 3 and the knock mechanism 4 of the knock type ballpoint pen 1 according to an embodiment of the present invention and a cutaway perspective view of the rear case 22. Fig. 5 is a cross-sectional perspective view of the rotor 42 of the knock type ballpoint pen 1 according to an embodiment of the present invention, where (a) is a cross-sectional perspective view and (b) is a view seen from the front side. Fig. 6 is a cross-sectional view of the rear case 22 of the knock type ballpoint pen 1 according to an embodiment of the present invention. The knock mechanism 4 includes a knock member 41 and a rotor 42 . An outer cam portion 222 is formed on the inner peripheral surface of the rear portion 22b of the rear case 22. The outer cam portion 222 is made up of three ridges 222a extending in the axial direction and arranged at equal intervals in the circumferential direction, and three slide grooves 222b between the three ridges 222a. The tips of the three ridges 222a are formed into inclined surfaces that are inclined in the axial direction when viewed from the outer circumferential direction (see FIG. 6). Through the action of the knock mechanism 4 and the outer cam portion 222, the ballpoint pen tip 31 at the tip of the ballpoint pen refill 3 appears and disappears from the tip opening 211 at the tip of the front case 21 in response to the user's knocking action.

[0013] The knock member 41 is a rear member of the knock mechanism 4, and is housed within the rear case 22 so as to be axially slidable. The knock member 41 is made up of a rear operating portion 411 and a front cam portion 412. An insertion hole is formed from the front end of the cam portion 412 to near the rear end of the operating portion 411 along the axis. The operation portion 411 protrudes from the rear end opening 221 of the rear case 22, and a user presses the knock member 41 to perform a knock operation. Cam portion 412 has cam surface 412a formed in a triangular mountain shape at its front end, which engages with a rear end portion of engaging protrusion 422a of engaging portion 422 of rotor 42 (described later) (see FIG. 4).

[0014] The rotor 42 is made up of a refill receiving portion 421 on the front side, an engaging portion 422 in the middle, and a protruding portion 423 on the rear side. The refill receiving portion 421 is the portion that receives the rear end portion of the ink tank 32 of the ballpoint pen refill 3, and is formed as a fitting hole having an inner diameter larger than the outer diameter of the ink tank 32 of the ballpoint pen refill 3, and the bottom surface 421a of the fitting hole abuts against the rear end surface of the ink tank 32. Bottom surface 421a is formed in an annular shape at the bottom of refill receiving portion 421. Bottom surface 421a is provided with three protrusions 421a1 protruding toward the center of the annular shape and three recesses 421a2 recessed toward the axial rear side, which are equally spaced apart (see FIG. 5). In this embodiment, refill receiving portion 421 is formed as a fitting hole, but it may have a structure that only has a surface (corresponding to bottom surface 421a) that abuts against the rear end portion of ink tank 32, rather than a fitting hole.

[0015] Three engaging protrusions 422a are formed at equal intervals in the circumferential direction on the outer circumferential surface of the engaging portion 422. The rear ends of the engaging protrusions 422a are formed into an inclined surface that is inclined in the axial direction when viewed from the outer circumferential direction, and the inner circumferential side thereof engages with the cam surface 412a of the cam portion 412. In addition, the outer circumferential side thereof engages with the front end side of the protrusions 222a formed on the inner circumferential surface of the rear case 22 or with the slide groove 222b.

[0016] The protrusion 423 is inserted into an insertion hole of the knock member 41, and connects the knock member 41 and the rotor 42 to be slidable relative to each other in the axial direction. A coil spring 43 is interposed between a step formed on the inner circumferential surface of the insertion hole of the cam portion 412 and a step formed on the outer circumferential surface of the boundary between the engagement portion 422 and the protrusion 423 of the rotor 42, for biasing them in a direction separating them from each other. The coil spring 43 biases the knock member 41 so as to protrude from the rear end opening 221 of the rear case 22.

[0017] [Knock mechanism operation] When the knock member 41 is pressed down in a state where the ballpoint pen tip 31 of the ballpoint pen refill 3 is recessed from the tip opening 211 of the front case 21 (the state shown in FIG. 2), the cam surface 412a at the tip of the knock member 41 abuts against the rear end of the engagement protrusion 422a of the rotor 42, moving the rotor 42 toward the tip side. At this time, the shape of the cam surface 412a and the shape of the inclined surface at the tip of the protrusion 222a of the rear case 22 cooperate with each other, so that the engagement protrusion 422a comes out of the slide groove 222b of the rear case 22 and the rotor 42 rotates. Then, the rotor 42 moves back slightly axially rearward together with the knock member 41, while the rotor 42 further rotates, and the rear end of the engagement protrusion 422a engages with the tip of the protrusion 222a, and the ballpoint pen tip 31 is held in a state protruding from the tip opening 211. Next, when the knock member 41 is pressed down, the cam surface 412a at the tip of the knock member 41 comes into contact with the rear end of the engagement protrusion 422a of the rotor 42, moving the rotor 42 toward the tip side. At this time, the shape of the cam surface 412a and the shape of the inclined surface at the tip of the protrusion 222a of the rear case 22 cooperate with each other, disengaging the cam surface 412a from the engagement protrusion 422a, and rotating the rotor 42. Then, the rotor 42 moves back largely axially rearward together with the knock member 41, while rotating further, and the rear end of the engagement protrusion 422a fits into the slide groove 222b, and the ballpoint pen tip 31 retracts from the tip opening 211.

[0018] As described above, the rotor 42 rotates around the axis due to the shape of the cam surface 412a and the shape of the inclined surface at the tip of the protrusion 222a cooperating with each other in response to the knocking action. In this embodiment, the rotor 42 is configured to rotate clockwise when viewed from the rear end side (see FIG. 3). Note that the rotor 42 may rotate counterclockwise instead of clockwise. The configurations and operations of the knock mechanism 4 and the outer cam portion 222 have been briefly described above, but since the knock mechanism 4 and the outer cam portion 222 of this embodiment have known configurations, detailed description thereof will be omitted.

[0019] [Eccentric structure] In this embodiment, the axis a of the ballpoint pen refill 3 and the axis b of the knock mechanism 4 are misaligned, that is, the ballpoint pen refill 3 has an eccentric structure. In order to realize this eccentric structure, in this embodiment, the axis a of the inner circumferential surface of the front portion 22a of the rear case 22 (concentric with the axis a of the front case 21) and the axis b of the inner circumferential surface of the rear portion 22b (the portion in which the knock mechanism 4 is housed) of the rear case 22 are made eccentric (see Figure 6). In this structure, the axis a of the ballpoint pen refill 3, which is held concentric with the axis a of the front case 21 near the tip of the front case 21, is also concentric with the axis a of the front portion 22a of the rear case 22. In contrast to this, since the axis b of the rear portion 22b of the rear case 22 is made eccentric, the axis b of the knock mechanism 4 housed therein is also eccentric with the axis a of the ballpoint pen refill 3. In Figs. 1 to 3, 6 and 7, the amount of eccentricity is indicated by X.

[0020] In this embodiment, in order to make the axis a of the inner peripheral surface of the front portion 22a of the rear case 22 eccentric to the axis b of the inner peripheral surface of the rear portion 22b of the rear case 22, the outer peripheral surface of the rear portion 22b is shifted (offset) toward the center of the rear portion 22b with respect to the outer peripheral surface of the front portion 22a, and the diameter (inner diameter) of the inner peripheral surface of the rear portion 22b is made smaller than the diameter (inner diameter) of the inner peripheral surface of the front portion 22a. The offset amount of the outer peripheral surface of the rear portion 22b with respect to the outer peripheral surface of the front portion 22a is indicated by Y in FIG. 1. In this embodiment, offset portion 22b1, which is a portion shifted toward the center of rear portion 22b, is formed by making a portion of the outer peripheral surface of rear case 22 into a flat surface that is recessed in the axial direction of rear case 22. However, offset portion 22b1 can also be formed by reducing the diameter of the outer peripheral surface of rear case 22 while keeping the shape of the cylinder, that is, by making the diameter of the outer peripheral surface of rear portion 22b of rear case 22 smaller than the diameter of the outer peripheral surface of front portion 22a (the diameter of the outer peripheral surface of front case 21).

[0021] [clip] The clip 5 is disposed at an offset portion 22b1 (see FIG. 3) which is a portion of the outer circumferential surface of the rear portion 22b shifted toward the center of the rear portion 22b with respect to the outer circumferential surface of the front portion 22a. The clip 5 is a so-called binder clip, and has a resin clip body 51 rotatably supported on a clip support portion 223 formed integrally with the outer peripheral surface of the offset portion 22b1, and a metal clip plate 52 inserted and fixed into the clip body 51 from the front side. The clip body 51 is inserted into the spring insertion hole 223a of the clip support portion 223, and the front side of the clip body 51 is biased in a direction approaching the outer peripheral surface of the rear case 22 by the compressed and attached coil spring 53. The tip side of clip plate 52 fixed to clip body 51 is also biased in a direction approaching the outer circumferential surface of rear case 22, and the tip side of clip plate 52 abuts against protrusion 224 formed on the outer circumferential surface of the offset portion. By pressing the rear end side of clip body 51 toward the outer circumferential surface against coil spring 53, the tip side of clip plate 52 is separated from protrusion 224, allowing clip 51 to clamp documents, pockets, etc. By locating the clip 5 at the offset portion 22b1, the height H (see Figures 1 and 2) of the knock-type ballpoint pen 1 at the point where the clip 5 protruding from the cylindrical case 2 is located can be reduced, reducing the overall size of the knock-type ballpoint pen 1, improving portability, and improving the design.

[0022] Incidentally, offset portion 22b1 does not necessarily have to be provided. By making the outer peripheral surface of front portion 22a of rear case 22 and the outer peripheral surface of rear portion 22b of rear case 22 flush with each other and increasing the thickness of a portion of rear portion 22b of rear case 22, the inner diameter of rear portion 22b of rear case 22 can be reduced so that axis b of the inner surface of rear portion 22b of rear case 22 is eccentric with axis a of the front portion. In addition, when the offset portion 22b1 is provided, the inner diameter of the rear portion 22b of the rear case 22 may be made the same as the inner diameter of the front portion 22a, and the outer peripheral surface of the rear portion 22b may be shifted (offset) radially outward from the outer peripheral surface of the front portion 22a on the opposite side of the direction perpendicular to the axial direction to the offset portion 22b1.

[0023] [Rotating ballpoint refill] As described above, the rotor 42 rotates with each knocking motion. When the rotor 42 rotates, the ballpoint pen refill 3, the rear end of which is in contact with the bottom surface 421a of the refill receiving portion 421 of the rotor 42, also rotates due to the frictional force between the bottom surface 421a and the rear end surface of the ink tank 32 (see FIG. 3). In addition, a step is formed by a recess 421a2 formed in the bottom surface 421a, and the corner of this step is adapted to catch on the rear end surface of the ink tank 32, so that the rotation of the rotor 42 is further transmitted to the ballpoint pen refill 3. 3 shows a state in which the outer peripheral surface of the ink tank 32 abuts against the inner peripheral surface of the refill receiving portion 421. In this state, since the inner peripheral surface of the refill receiving portion 421 and the outer peripheral surface of the ink tank 32 abut against each other, the frictional force generated at this abutment surface also serves to transmit the rotation of the rotor 42 to the rotation of the ballpoint pen refill 3. Depending on the amount of eccentricity X, the outer diameter of the ink tank 32, the inner diameter of the refill receiving part 421, etc., the outer peripheral surface of the ink tank 32 and the inner peripheral surface of the refill receiving part 421 may not come into contact with each other. Also, because the ink tank 32 of the ballpoint pen refill 3 is made of a soft resin, it may bend depending on how the knock type ballpoint pen 1 is used, and the degree of this bending may change the degree of contact between the outer peripheral surface of the ink tank 32 and the inner peripheral surface of the refill receiving part 421.

[0024] 7A and 7B are diagrams for explaining the operation of the knock-type ballpoint pen 1 according to the embodiment of the present invention, where (a) shows the embodiment and (b) shows a conventional one. The portion of the bottom surface 421a shown with diagonal lines is the surface that actually comes into contact with the rear end of the ink tank 32 (shown with a dotted line in FIG. 7). The rotation of rotor 42 being transmitted to ballpoint pen refill 3, causing ballpoint pen refill 3 to rotate, can also occur in a conventional knock-type ballpoint pen in which the axis of the entire knock mechanism and the axis of the refill are arranged concentrically. As shown in FIG. 7(b), in a conventional knock-type ballpoint pen, the axis b of the bottom surface 421a (knock mechanism 4) and the axis a of the ink tank 32 (ballpoint pen refill 3) are concentric, so that the arc-shaped surface at the rear end of the ink tank 32 (ballpoint pen refill 3) abuts against the bottom surface 421a almost evenly, although only by a narrow width.

[0025] 7(a), in this embodiment, the axis b of the bottom surface 421a (knocking mechanism 4) and the axis a of the ink tank 32 are eccentric, so that the rear end of the ink tank 32 comes into contact widely on the eccentric side, and the opposite side hardly comes into contact at all. As a result, on the eccentric side, the ink tank 32 comes into contact up to the outer periphery of the bottom surface 421a, so that the large frictional force causes the ink tank 32 to rotate more strongly. Then, in the eccentric structure of this embodiment, the rotation of the bottom surface 421a (knocking mechanism 4) is more likely to be strongly transmitted to the ink tank 32 (ballpoint pen refill 3) than in the conventional concentric structure. Furthermore, in the eccentric structure of this embodiment, the inner surface of the refill receiving portion 421 and the outer surface of the ink tank 32 are more likely to come into contact with each other than in the conventional concentric structure, so that the rotation of the refill receiving portion 421 (knock mechanism 4) is more easily transmitted to the ink tank 32 (ballpoint pen refill 3). From the above, in the eccentric structure of this embodiment, the rotation of the knock mechanism 4 is more easily transmitted to the ballpoint pen refill 3 than in the conventional concentric structure, so that the ballpoint pen refill 3 is more likely to rotate due to the knocking action. Therefore, the ballpoint pen refill 3 rotates with each knocking action, and the position where the ballpoint pen tip 31 contacts the writing surface during writing changes. Due to this action, in this embodiment, uneven wear of the ballpoint pen tip 31 can be more effectively suppressed.

[0026] [Variations] FIG. 8 is a diagram of a rotor 42 according to a modified embodiment of the present invention. In this modification, the shape of bottom surface 421a of refill receiving portion 421 is different from that of the above-described embodiment. Bottom surface 421a is formed in a partially cut-out circular shape at the bottom of refill receiving portion 421. Bottom surface 421a is provided with three protrusions 421a1 protruding toward the center of the circular shape and three cut-outs 421a3, which are cut out, at equal intervals. Moreover, protrusion 421a1 and its outer periphery are formed into an inclined surface that inclines from bottom surface 421a from the downstream side in the rotation direction of refill receiving portion 421 (knock mechanism 4) to the upstream side in the rotation direction. This inclined surface forms a bent portion at the boundary between the downstream end of the inclined surface in the rotation direction and the flat surface. Also, a step is formed at the boundary between the upstream end of the inclined surface in the rotation direction and the flat surface of bottom surface 421a. The corners of these bent portions and steps, as well as the corners of the boundary between bottom surface 421a and notch portion 421a3, are adapted to catch on the rear end surface of ink tank 32, so that the rotation of rotor 42 can be transmitted to ballpoint pen refill 3 more strongly.

[0027] In the above embodiment and modified examples, a binder clip is used as the clip 5, but it may be a clip that does not open or close. Also, instead of the configuration consisting of the resin clip body 51 and the metal clip plate 52, the entire clip may be molded from resin or metal. Furthermore, the writing instrument may be any type of writing instrument, and in addition to a ballpoint pen as in the above-described embodiment, it may be a felt-tip pen, a marker, etc., and may be any writing instrument that protrudes and retracts from the tip of a cylindrical case by a knock mechanism. In particular, in the case of writing instruments such as ballpoint pens whose tip is symmetrical about the axis, for example, felt-tip pens and markers that use bullet-shaped tips, uneven wear of the tip can be more effectively prevented by rotating the refill with each knock operation.

[0028] The knock-type ballpoint pen 1 according to the embodiment and modified examples of the present invention have been described in detail above with reference to the drawings. However, the specific configuration is not limited to these embodiments and modified examples, and the present invention also includes design changes that do not deviate from the gist of the present invention. [Explanation of symbols]

[0029] 1. Knock-type ballpoint pen 2 Cylindrical case 21 Front case 211 Tip opening 22 Rear case 22a Front side 22b Rear side 22b1 Offset section 221 Rear end opening 222 Outer cam part 222a Projection 222b Slide groove 223 Clip support 223a Spring insertion hole 224 Protrusion 3 Ballpoint pen refills 31 Ballpoint Pen Tip 32 Ink tank 4 Knock mechanism 41 Knock parts 411 Operation section 412 Cam section 412a Cam surface 42 Rotor 421 Refill receiver 421a Bottom 421a1 Protrusion 421a2 Recess 421a3 Notch 422 Engagement part 422a Engagement protrusion 423 Protrusion 43 Coil Spring 5 Clips 51 Clip body 52 Clip Board 53 Coil Spring a) Ballpoint pen refill 3, axis of front part 22a of rear case 22 b) Axial center of the rear part 22b of the rear case 22 and the knock mechanism 4

Claims

1. A knock-type writing instrument in which a knock mechanism and a refill are housed in a cylindrical case, The knock mechanism has a rotor that rotates in response to a knock action, The axis of the rotor is eccentric with respect to the axis of the refill. A knock-type writing instrument characterized by the above.

2. 2. The knock-type writing instrument according to claim 1, characterized in that the axis of the inner circumferential surface of the portion housing the knock mechanism at the rear end of the cylindrical case is eccentric with respect to the axis of the inner circumferential surface of the other portion of the cylindrical case.

3. 3. The knock-type writing instrument according to claim 2, wherein a part of the outer peripheral surface of the portion housing the knock mechanism at the rear end side of the cylindrical case is formed into a flat surface recessed in the axial direction of the cylindrical case.

4. 3. The knock-type writing instrument according to claim 2, wherein the axis of the outer peripheral surface of the portion housing the knock mechanism at the rear end side of the cylindrical case is eccentric with respect to the axis of the outer peripheral surface of the other portion of the cylindrical case.

5. 4. The knock-type writing implement according to claim 3, wherein a clip is provided on the flat surface.

6. A clip is provided on the outer peripheral surface of the rear end of the cylindrical case, 5. The knock-type writing implement according to claim 4, wherein the axis of the outer peripheral surface of the portion housing the knock mechanism is eccentric in a direction away from the clip with respect to the axis of the outer peripheral surface of the other portion.

7. The knock-type writing instrument according to any one of claims 1 to 6, characterized in that the inner diameter of a portion of the rear end of the cylindrical case that houses the knock mechanism is smaller than the inner diameter of the other portions of the cylindrical case.

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