Abstract:
A writing implement ( 1 ) wherein the outer circumferential surface of a crown outer cylindrical section ( 21 ) fits into the inner circumferential surface of a case ( 11 ) and the inner circumferential surface of a crown inner cylindrical section ( 22 ) fits into the outer circumferential surface of an attachment body ( 12 ). In addition, an annular space ( 27 ) is formed in the crown ( 5 ), between the inner circumferential surface of the crown outer cylindrical section ( 21 ) and the outer circumferential surface of the crown inner cylindrical section ( 22 ). Air will flow through the annular space ( 27 ) even if, for example, the cap ( 2 ) becomes stuck in the bronchial tubes of an infant as a result of being accidentally swallowed by the infant. Suffocation accidents can, therefore, be reliably prevented.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a National Stage application of PCT/JP2012/064476, filed Jun. 5, 2012. 
     TECHNICAL FIELD 
     The present invention relates to a cap for a writing instrument and to a writing instrument. 
     BACKGROUND ART 
     For example, at the front end of a cap body or the back end of a writing instrument body, an endcap which has a function as decoration of the writing instrument or a function as a pedestal for a clip is attached (Japanese Patent Publication No. 2009-214515A, Japanese Patent Publication No. 2010-247405A, and Japanese Patent Publication No. 11-221997A). For example, in Japanese Patent Publication No. 2009-214515A, an endcap is attached to a projection which is arranged in a restricting wall part which is formed at a top end of a cylinder. In attachment, an inside circumferential surface of a mounting hole of the endcap is fit with an outside circumferential surface of the projection. The endcap is attached to the cylinder by a predetermined mounting strength in this way. 
     SUMMARY OF INVENTION 
     In general, the overall length of a writing instrument is determined as a predetermined size. The front end of the writing instrument body enters into the cap, so to avoid interference with the writing instrument body, the length by which the endcap enters the cap body cannot be made that large. Furthermore, the above-mentioned endcap is attached to the projection by just the inside circumferential surface of the mounting hole. Further, the outside diameter of the writing instrument is also determined as a predetermined size, so it is not possible to increase the outside diameters of the cap body and the endcap for the purpose of increasing the contact area of the cap body and endcap. As a result, in the above-mentioned endcap, sufficient mounting strength cannot be secured. In addition, in Japanese Patent Publication No. 2009-214515A, an air passage to be formed for the purpose of preventing suffocation when for example the cap is mistakenly swallowed is not considered at all. 
     The present invention was made in consideration of the above situation and has as its object the provision of a cap for a writing instrument and of a writing instrument which enable a sufficient mounting strength of the endcap to be secured and enable an air passage for flow of air to be secured. 
     To achieve the above object, according to the present invention, there is provided a writing instrument which is provided with an endcap which is provided with an endcap outer cylinder and an endcap inner cylinder, an inside circumferential surface of the endcap outer cylinder being arranged separate from an outside circumferential surface of the endcap inner cylinder whereby a ring-shaped space is formed between the inside circumferential surface of the endcap outer cylinder and the outside circumferential surface of the endcap inner cylinder, and a body which is provided with a cylinder and a tubular mount which is formed inside of the cylinder and which is connected to the cylinder and which forms a holding space for holding the endcap between an inside circumferential surface of the cylinder and an outside circumferential surface of the mount, wherein the endcap is inserted into the holding space of the body, an outside circumferential surface of the endcap outer cylinder and the inside circumferential surface of the cylinder are fit together, and an inside circumferential surface of the endcap inner cylinder and the outside circumferential surface of the mount are fit together, whereby the endcap is fastened to the body and air can flow between an inside of the body and an outside of the endcap through the ring-shaped space which is formed between the inside circumferential surface of the endcap outer cylinder and the outside circumferential surface of the endcap inner cylinder. 
     According to such a writing instrument, the endcap is fastened to the body by the outside circumferential surface of the endcap outer cylinder and the inside circumferential surface of the endcap inner cylinder being respectively fit together with the inside circumferential surface of the cylinder and the outside circumferential surface of the mount. As a result, even without setting the total length or outside diameter of the writing instrument large, for example, the endcap can be fastened to the body by a sufficient mounting strength compared with the case where it is fastened to the body by only the inside circumferential surface of the endcap inner cylinder. Further, the ring-shaped space which is formed between the inside circumferential surface of the endcap outer cylinder and the outside circumferential surface of the endcap inner cylinder establishes an air passage. As a result, air can flow through this air passage between the inside of the body and the outside of the endcap. Occurrence of accidents involving suffocation can therefore be reliably prevented. 
     In the writing instrument according to the present invention, the mount sticks out to the outside from the outside end of the endcap inner cylinder. By such a constitution, it is possible to give a decorative feature to the writing instrument by exposure of the mount to the outside. Further, a user can visually confirm the mount from outside. For example, by setting the color of the mount and the color type of the writing instrument the same, a user can simply confirm the color type of the writing instrument. Further, when the endcap is integrally formed with a clip of the same color type as the color type of the writing instrument, the user can confirm the color type of the writing instrument by the clip as well. 
     Further, the writing instrument according to the present invention is further provided with a cutaway part which is formed at an inside end of the endcap outer cylinder and forms an air passage between the inside circumferential surface of the cylinder and the outside circumferential surface of the mount. According to such a constitution, the inside end of the endcap outer cylinder can greatly enter the inside of the cylinder at the outside of the cutaway part. The total length and outside diameter of the writing instrument are restricted to predetermined sizes, so the space inside of the cylinder can be effectively used. Further, the outside circumferential surface of the endcap outer cylinder can contact the inside circumferential surface of the cylinder over a large area. In the endcap, a further large mounting strength is secured. 
     Further, in the writing instrument according to the present invention, the body is provided with a cap body which has the cylinder and the mount and a writing instrument is attached to the cylinder. 
     Further, according to the present invention, there is provided a cap for a writing instrument provided with an endcap which is provided with an endcap outer cylinder and an endcap inner cylinder, an inside circumferential surface of the endcap outer cylinder being arranged separate from an outside circumferential surface of the endcap inner cylinder, whereby a ring-shaped space is formed between the inside circumferential surface of the endcap outer cylinder and the outside circumferential surface of the endcap inner cylinder, and a cap body which is provided with a cylinder and a tubular mount which is formed inside of the cylinder and which is connected to the cylinder and which forms a holding space for holding the endcap between an inside circumferential surface of the cylinder and an outside circumferential surface of the mount, wherein the endcap is inserted into the holding space of the cap body, an outside circumferential surface of the endcap outer cylinder and the inside circumferential surface of the cylinder are fit together, and an inside circumferential surface of the endcap inner cylinder and the outside circumferential surface of the mount are fit together, whereby the endcap is fastened to the cap body and air can circulate between an inside of the cap body and an outside of the endcap through the ring-shaped space which is formed between the inside circumferential surface of the endcap outer cylinder and the outside circumferential surface of the endcap inner cylinder. 
     According to the present invention, it is possible to provide a cap for a writing instrument and a writing instrument which enable sufficient mounting strength of the endcap to be secured and enable an air passage for flow of air to be secured even without setting the overall length or outside diameter of the writing instrument large. Further, the mount to which the endcap is attached is exposed to the outside, so it is possible to give a decorative feature to the writing instrument and possible for a user to simply confirm the color of the writing instrument from the outside. 
     Below, the present invention will be able to be further understood from the attached drawings and the description of the preferred embodiments of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a side view which schematically shows the constitution of a writing instrument according to a first embodiment of the present invention. 
         FIG. 2  is a vertical cross-sectional view which schematically shows the constitution of a writing instrument according to a first embodiment of the present invention. 
         FIG. 3  is a vertical cross-sectional view which schematically shows the constitution of a cap for a writing instrument according to a first embodiment of the present invention. 
         FIG. 4  is a cross-sectional view along a line  4 - 4  of  FIG. 3 . 
         FIG. 5  is a partial enlarged vertical cross-sectional view which schematically shows the constitution of a cap for a writing instrument according to a first embodiment of the present invention. 
         FIG. 6  is a cross-sectional view along a line  6 - 6  of  FIG. 5 . 
         FIG. 7  is a cross-sectional view along a line  7 - 7  of  FIG. 5 . 
         FIG. 8  is a cross-sectional view along a line  8 - 8  of  FIG. 7 . 
         FIG. 9  is a side view which schematically shows the constitution of an endcap for a writing instrument according to a first embodiment of the present invention. 
         FIG. 10  is another cross-sectional view which schematically shows the constitution of a cap for a writing instrument according to a first embodiment of the present invention. 
         FIG. 11  is a side view which schematically shows the constitution of a writing instrument according to a second embodiment of the present invention. 
         FIG. 12  is a vertical cross-sectional view which schematically shows the constitution of a writing instrument according to a second embodiment of the present invention. 
         FIG. 13  is a perspective view of a clip according to a second embodiment of the present invention. 
         FIG. 14  is a perspective view of an endcap according to a second embodiment of the present invention. 
         FIG. 15  is a side cross-sectional view of an endcap according to a second embodiment of the present invention. 
         FIG. 16  is a top view of an endcap according to a second embodiment of the present invention. 
         FIG. 17  is a perspective view of a cap body according to a second embodiment of the present invention. 
         FIG. 18  is a side cross-sectional view of a cap body according to a second embodiment of the present invention. 
         FIG. 19  is a top view of a cap body according to a second embodiment of the present invention. 
         FIG. 20  is a side view of a clip and endcap according to a second embodiment of the present invention. 
         FIG. 21  is an enlarged vertical cross-sectional view of a front end part of a cap according to a second embodiment of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Below, referring to the attached drawings, embodiments of the present invention will be explained. Further, in the attached figures, the same or similar components are assigned the same reference notations. 
     First, referring to  FIGS. 1 to 10 , a first embodiment of the present invention will be explained. 
       FIG. 1  is a side view which schematically shows the constitution of a writing instrument  1  according to a first embodiment of the present invention. The writing instrument  1  is, for example, a water-based ink ball point pen. The writing instrument  1  is provided with a cap  2  and a writing instrument body  3  which is inserted from a back end of the cap  2  and is attached to the cap  2 . The cap  2  is provided with a cap body  4  which receives a front end part of the writing instrument body  3  at its back end, an endcap  5  which is fastened by insertion into a front end of the cap body  4 , and a clip  6  which is integrally formed with the endcap  5 . The clip  6  passes through the cutaway part  7  which is formed at the front end of the cap body  4  and sticks out to outside of the cap body  4 . The endcap  5  has a function as decoration of the writing instrument  1  and a function as a pedestal of the clip  6 . Note that, in this Description, the front end of the writing instrument body  3 , that is, the front side of the pen, is defined as the “front” side of the writing instrument body  3  while the side opposite to the front of the pen of the writing instrument body  3  along the axial center of the writing instrument body  3  is defined as the “back” side of the writing instrument body  3 . 
       FIG. 2  is a vertical cross-sectional view along an imaginary plane which includes the axial center of the writing instrument  1 . Referring to  FIG. 2  as well, the writing instrument body  3  is provided with a refill  8  which holds ink and has a tip at its front end and a back shaft  9  which receives a back end part of the refill  8  and is attached to the refill  8 . The refill  8  is filled with a water-based ink. On the other hand, the cap body  4  of the cap  2  is provided with a round tubular shaped cylinder  11  and a mount  12  which is arranged inside of the cylinder  11  and is connected to the cylinder  11 . The cylinder  11  and the mount  12  are arranged coaxially with each other. The cylinder  11  receives the front end part of the refill  8  at its back end and receives the endcap  5  at its front end. Note that, in this Description, the side where the endcap  5  is attached is defined as the “front” side of the cap body  4 , while the side where the writing instrument body  3  is inserted is defined as the “back” side of the cap body  4 . 
     The refill  8  and back shaft  9  which form the writing instrument body  3 , the cylinder  11  and mount  12  which form the cap body  4 , and the endcap  5  and clip  6  are respectively, for example, formed from polycarbonate (PC), acrylonitrile butadiene styrene (ABS), polypropylene (PP), polyacetal (POM), acryl, polyethylene terephthalate (PET), polyethylene (PE), or another resin material. Further, the cylinder  11  and mount  12  are formed by one-piece molding. Similarly, the endcap  5  and clip  6  are formed by one-piece molding. 
       FIG. 3  is a partial enlarged vertical cross-sectional view of a cap  2 . As shown in  FIG. 3 , the cylinder  11  is formed from a cylindrically shaped hollow member which is open at its both ends. The mount  12  is arranged inside of the cylinder  11  near the front end of the cylinder  11 . The outside circumferential surface of the mount  12  is arranged separated from the inside circumferential surface of the cylinder  11 . The mount  12  has a columnar large diameter part  13  which is arranged at a back end side of the cylinder  11 , a columnar small diameter part  14  which is formed to a smaller diameter than the large diameter part  13  and is arranged at a front end side of the cylinder  11 , and a taper part  15  which is arranged between a front end of the large diameter part  13  and a back end of the small diameter part  14  and connects the large diameter part  13  and the small diameter part  14 . The diameter of the taper part  15  decreases the further from the large diameter part  13  to the small diameter part  14 . The large diameter part  13 , small diameter part  14 , and taper part  15  are integrally formed. At the back end of the large diameter part  13 , a holding space  16  is formed for holding the tip of the refill  8  in an air-tight state. The holding space  16  is formed from a closed bottom hole. 
       FIG. 4  is an end face view along a line  4 - 4  of  FIG. 3 . Referring to  FIG. 4  as well, the mount  12  is, for example, connected by four ribs  17  to the inside circumferential surface of the cylinder  11 . The ribs  17  are formed integrally with the inside circumferential surface of the cylinder  11  and the outside circumferential surface of the large diameter part  13  of the mount  12 . Here, the ribs  17  are arranged around the axial center of the writing instrument  1  at 90° angular intervals at equal intervals from each other. In this way, at the outsides of the ribs  17 , a ring-shaped space, that is, an inside air passage  18 , is formed between the inside circumferential surface of the cylinder  11  and the outside circumferential surface of the large diameter part  13 . The inside air passage  18  enables air to flow between the front end and back end of the cylinder  11 . At the same time, the inside air passage  18  is connected to the outside air passage which is formed in the endcap  5  explained later. 
     On the other hand, as will be clear from  FIG. 3 , between the outside circumferential surfaces of the large diameter part  13 , the small diameter part  14 , and the taper part  15  of the mount  12  and the inside circumferential surface of the cylinder  11 , a holding space  19  for holding the endcap  5  is formed. The endcap  5  is provided with a for example round tubular shaped endcap outer cylinder  21  which is arranged inside the holding space  19  and a for example round tubular shaped endcap inner cylinder  22  which is arranged inside the endcap outer cylinder  21 . The outside circumferential surface of the endcap inner cylinder  22  is arranged separated from the inside circumferential surface of the endcap outer cylinder  21 . The endcap  5  is arranged coaxially with the cap body  4 . The endcap inner cylinder  22  is arranged near the outside end of the endcap outer cylinder  21 . The outside end of the endcap inner cylinder  22  which is exposed to the outside at the front end of the cap body  4  is arranged at the outside from the outside end of the endcap outer cylinder  21  along the axial center of the cap body  4 . The endcap outer cylinder  21  engages with the inside circumferential surface of the cylinder  11  at the outside circumferential surface. The endcap inner cylinder  22  engages with the outside circumferential surface of the small diameter part  14  of the mount  12  at the inside circumferential surface. That is, the endcap  5  engages with the cap body  4  at two locations. The inside end of the endcap outer cylinder  21  extends up to the front of the above-mentioned ribs  17 . In this way, the inside end of the outer cylinder  21  enters the above-mentioned inside air passage  18 . 
       FIG. 5  is a partial enlarged vertical cross-sectional view of the front end of the cap  2 . At the outside circumferential surface of the endcap outer cylinder  21 , a ring-shaped endcap side engagement part  23  which extends without interruption about the axial center of the endcap outer cylinder  21  is formed. The endcap side engagement part  23  sticks out from the outside circumferential surface of the endcap outer cylinder  21 . The endcap side engagement part  23  is formed at the inside circumferential surface of the cylinder  11  and rides over the ring-shaped cap side engagement part  24  which extends without interruption about the axial center of the cylinder  11  to engage with the cap side engagement part  24 . The cap side engagement part  24  sticks out from the inside circumferential surface of the cylinder  11 . In this way, the endcap  5  is restricted from detaching from the front end of the cylinder  11 . In addition, at the outside end of the endcap outer cylinder  21 , an outside flange  25  is formed which extends without interruption about the axial center of the end cap outer cylinder  21 . The outside flange  25  contacts the end face of the front end of the cylinder  11 . At the outside circumferential surface of the endcap outer cylinder  21 , the above-mentioned clip  6  is integrally connected. 
     The front end, that is, the outside end, of the small diameter part  14  of the mount  12  sticks out to the outside from the outside end of the endcap inner cylinder  22 . The endcap inner cylinder  22  is attached to only the small diameter part  14 . The endcap outer cylinder  21  and the endcap inner cylinder  22  are for example connected with each other by four ribs  26 . The ribs  26  are formed integrally at the inside circumferential surface of the endcap outer cylinder  21  and the outside circumferential surface of the endcap inner cylinder  22 .  FIG. 6  is an end face view along the line  6 - 6  of  FIG. 5 . Referring to FIG.  6  together, the ribs  26  are arranged about the axial center of the writing instrument  1  at 90° angular intervals at equal intervals from each other. In this way, at the outsides of the ribs  26 , a ring-shaped space, that is, outside air passage  27 , is formed between the inside circumferential surface of the endcap outer cylinder  21  and the outside circumferential surface of the endcap inner cylinder  22 . The outside air passage  27  enables the flow of air between the inside of the cap body  4  and the outside of the endcap  5 . Note that, the angular positions of the ribs  26  are, for example, set the same as the angular positions of the ribs  17  about the axis of the cap body  4 . However, the angular positions of the ribs  26  may also be offset from the angular positions of the ribs  17 . 
     As clear from  FIG. 5 , the ribs  26  are provided with extended parts  26   a  which extend along the inside circumferential surface of the endcap outer cylinder  21  toward the inside end of the endcap outer cylinder  21 . That is, the extended parts  26   a  extend toward the inside from the inside end of the endcap inner cylinder  22 . The inside ends of the extended parts  26   a  are interrupted at positions retracted from the inside end of the endcap outer cylinder  21  to the outside end side of the endcap outer cylinder  21 . Parts of the extended parts  26   a  are stopped at the outside circumferential surface of the large diameter part  13 . That is, the extended parts  26   a  of the ribs  26  contact the large diameter part  13 . Such extended parts  26   a , as explained later, contribute to improvement of the mounting strength of the endcap  5 . 
       FIG. 7  is a cross-sectional view along the line  7 - 7  of  FIG. 5 . As shown in  FIG. 7 , at the inside end of the endcap outer cylinder  21 , cutaway parts  28  are formed about the axial center of the endcap outer cylinder  21  in predetermined angular ranges. Referring to  FIG. 8  and  FIG. 9  together, at the inside end of the endcap outer cylinder  21 , two cutaway parts  28  are formed axially symmetrically about the axial center of the endcap outer cylinder  21 . Inside the cutaway parts  28 , an inside air passage  18  is secured. The inside ends of the cutaway parts  28  are arranged closer to the outside end of the endcap outer cylinder  21  than the front end of the large diameter part  13 . As a result, due to the action of the cutaway parts  28 , the inside air passage  18  and the connection path  29  which is formed between the endcap outer cylinder  21 , and small diameter part  14  and taper part  15  are connected with each other. The connection path  29  is connected together with the outside air passage  27 . As a result, the outside air passage  27  and the inside air passage  18  are connected with each other through the connection path  29 . 
     In such a writing instrument  1 , the outside circumferential surface of the endcap outer cylinder  21  engages with the inside circumferential surface of the cylinder  11  and the inside circumferential surface of the endcap inner cylinder  22  engages with the outside circumferential surface of the mount  12 . Therefore, for example, if stress acts on the endcap  5  in a direction wherein the axial center of the endcap  5  becomes slanted from the axial center of the cylinder  11 , for example, the outside circumferential surface of the endcap outer cylinder  21  and the inside circumferential surface of the endcap inner cylinder  22  will be respectively pressed against the inside circumferential surface of the cylinder  11  and the outside circumferential surface of the mount  12  while pivoting about the front end of the cylinder  11 . As a result, slanting of the endcap  5  will be restricted. Therefore, even if not setting the total length or outside diameter of the writing instrument  1  large, the endcap  5  can be attached to the cap body  4  with sufficient mounting strength compared with for example the case of being received at the mount  12  only at the inside circumferential surface of the endcap inner cylinder  22 . 
     In addition, inside the cap body  4 , an inside air passage  18  is secured by the cutaway parts  28  which are formed at the inside end of the endcap outer cylinder  21 . At the same time, the inside end of the endcap outer cylinder  21  can enter largely into the cylinder  11  at the outside of the cutaway parts  28 . For this reason, even when the total length and outside diameter of the writing instrument  1  are limited, the space inside the cylinder  11  can be effectively used. Further, the outside circumferential surface of the endcap outer cylinder  21  contacts the inside circumferential surface of the cylinder  11  over a large area. For example, as clear from  FIG. 5 , the extended parts  26   a  of the ribs  26  are stopped at the outside circumferential surface of the large diameter part  13 . That is, at the parts of the extended parts  26   a , the thickness of the endcap outer cylinder  21  matches the interval between the inside circumferential surface of the cylinder  11  and the outside circumferential surface of the large diameter part  13 , so at the endcap  5 , a further larger mounting strength can be secured. 
     Furthermore, at the endcap  5 , an outside air passage  27  is formed between the inside circumferential surface of the endcap outer cylinder  21  and the outside circumferential surface of the endcap inner cylinder  22 . As a result, for example, even if a child mistakenly swallows the cap  2  and it becomes lodged in the trachea of the child, for example, as shown in  FIG. 10 , air can flow from the front end of the cap  2 , that is, from the outside air passage  27 , through the connection path  28  and inside air passage  18  to the back end of the cap  2 , that is, the back end of the cylinder  11 . Conversely, air can flow from the back end of the cap  2 , that is, the back end of the cylinder  11 , through the inside air passage  18  and connection path  29  to the front end of the cap  2 , that is, the outside air passage  27 . Therefore, occurrence of accidents leading to suffocation can be reliably prevented. 
     Further, the mount  12  is formed integrally with the cylinder  11 , so the mount  12  can be simply formed to the same color as the cylinder  11 . The small diameter part  14  of the mount  12  sticks out to the outside from the outside end of the endcap inner cylinder  22 , so the writing instrument  1  can be given a design feature. Further, a user can see the mount  12  at the front end of the cap  2 . Therefore, for example, when the ink which is filled in the refill  8  and the cylinder  11  and mount  12  are formed from the same color, the user can confirm the color type of the writing instrument  1  even if viewing the writing instrument  1  from only the front end of the cap  2 . Further, if a clip  6  of the same color type as the color type of the writing instrument  1  is integrally formed, the user can confirm the color type of the writing instrument by the clip  6  as well. Further, the mount  12  is formed integrally with the cylinder  11 , so in the writing instrument  1 , an increase in the number of parts can be avoided. 
     Next, referring to  FIGS. 11 to 21 , a second embodiment of the present invention will be explained. 
       FIG. 11  is a side view which schematically shows the constitution of the writing instrument  1  according to the second embodiment of the present invention. The writing instrument  1  is, for example, a water-based ink ball point pen. The writing instrument  1  is provided with a cap  2  and a writing instrument body  3  which is inserted from the back end of the cap  2  to be attached to the cap  2 . The cap  2  is provided with a cap body  40  which receives a front end part of the writing instrument body  3  at its back end, an endcap  50  which is fastened by insertion into the front end of the cap body  40 , and a clip  60  which is fastened by one end part being inserted into the endcap  50 . 
       FIG. 12  is a vertical cross-sectional view along an imaginary plane which includes an axial center of the writing instrument  1 . The writing instrument body  3  is provided with a refill  8  which holds ink and has a tip at its front end and a back shaft  9  which receives the back end part of the refill  8  to be attached to the refill  8 . The refill  8  is filled with water-based ink. On the other hand, the cap body  40  of the cap  2  is provided with a round tubular shaped cylinder  11  and a mount  12  which is arranged inside of the cylinder  11  and is connected to the cylinder  11 . The cylinder  11  and the mount  12  are arranged coaxially with each other. The cylinder  11  receives the front end part of the refill  8  at its back end and receives the endcap  50  and clip  60  at its front end. 
     Below, the second embodiment will be explained in further detail, but explanations of features similar to the first embodiment will be omitted. 
     In the present embodiment, the clip  60  is a separate member from the endcap  50  and is formed from a material, that is, metal, different from the endcap  50 . In this case, the clip  60  is easily produced by pressing from a single sheet of metal. By being formed from a metal, the clip  60  is increased in strength and the writing instrument  1  can be given a design feature. However, the clip  60  may also be formed from a resin material the same or separate from the endcap  50 . 
       FIG. 13  is a perspective view of a clip  60  according to the present embodiment.  FIGS. 14 to 16  are respectively a perspective view, side cross-sectional view, and top view of an endcap  50  according to the present embodiment.  FIGS. 17 to 19  are respectively a perspective view, side cross-sectional view, and top view of a cap body  40  according to the present embodiment. The clip  60  has an insertion end part  61  which is bent substantially perpendicularly two times and an arc shaped end part  62  which is bent into an arc shape. The insertion end part  61  is press-fit into a through hole  51  which is formed in the front end of the endcap  50  to be engaged with the inside circumferential surface of the cylinder  11  of the cap body  40 . Further, the insertion end part  61  has four projecting parts  63  which project out in the width direction. The arc shaped end part  62  contacts a projection  41  which is provided on the outside circumferential surface of the cap body  40 . The projection  41  of the cap body  40  has the function of preventing the cap body  40  from breaking by contact with the clip  60 . 
     In the present embodiment, the endcap outer cylinder  21  and the endcap inner cylinder  22  of the endcap  50  are mutually connected by three ribs  26 . The ribs  26  are integrally formed at the inside circumferential surface of the endcap outer cylinder  21  and the outside circumferential surface of the endcap inner cylinder  22 . The ribs  26  are arranged about the axial center of the writing instrument  1  at 120° angular intervals at equal intervals from each other. The rib  26  near the through hole  51  has a thicker width in the circumferential direction than the other ribs  26  so that the outside air passage  27  and through hole  51  are formed. Similarly, the mount  12  of the cap body  40  is connected by three ribs  17  to the inside circumferential surface of the cylinder  11 . The ribs  17  are integrally formed at the inside circumferential surface of the cylinder  11  and the outside circumferential surface of the large diameter part  13  of the mount  12 . The ribs  17  are arranged about the axial center of the writing instrument  1  at 120° angular intervals at equal intervals from each other. The angular positions of the ribs  17  are set so that when the endcap  50  is fastened to the cap body  40 , they become the same as the angular positions of the ribs  26  of the endcap  50  about the axial center of the cap body  40 . Further, the three ribs  17  have equal widths. However, the numbers and angular intervals of the ribs  26  and  17  are not limited to three and 120°. The angular positions of the ribs  17  and the angular positions of the ribs  26  may also be offset. 
     Next, the method of assembly of the clip  60 , the endcap  50 , and the cap body  40  will be explained. 
     As shown in  FIG. 20 , first, the insertion end part  61  of the clip  60  is press-fit into the through hole  51  of the endcap  50  whereby the clip  60  is fastened to the endcap  50 . After fastening, even if force is applied to the clip  60  in a direction wherein the insertion end part  61  would detach from the through hole  51 , since the horizontal widths of the two projecting parts  63  (see  FIG. 13 ) at the front end side of the insertion end part  61  are greater than the horizontal width of the through hole  51 , these two projecting parts  63  will engage with the surroundings  52  of the through hole  51  so detachment of the clip  60  from the endcap  50  will be prevented. 
     Next, the endcap  50  which is provided with the clip  60  is fastened by insertion into the front end of the cap body  40  in a state with the top end part  53  of the endcap  50  (see  FIGS. 14 and 15 ) aligned with the cutaway part  7  of the cap body  40 .  FIG. 21  is an enlarged vertical cross-sectional view of a cap  2  according to the present embodiment. As shown in  FIG. 21 , if the endcap  50  provided with the clip  60  is inserted into the front end of the cap body  40 , the outside circumferential surface of the endcap outer cylinder  21  will engage with the inside circumferential surface of the cylinder  11  and the inside circumferential surface of the endcap inner cylinder  22  will engage with the outside circumferential surface of the mount  12 . Further, the insertion end part  61  of the clip  60  which sticks out from the through hole  51  of the endcap  50  will engage with the inside circumferential surface of the cylinder  11 . 
     Therefore, for example, if stress acts on the endcap  50  in a direction wherein the axial center of the endcap  50  becomes slanted from the axial center of the cylinder  11 , the outside circumferential surface of the endcap outer cylinder  21  and the insertion end  61  of the clip  60 , and the inside circumferential surface of the endcap inner cylinder  22  will be respectively pressed against the inside circumferential surface of the cylinder  11  and the outside circumferential surface of the mount  12  while pivoting about the front end of the cylinder  11 . As a result, slanting of the endcap  50  and clip  60  will be restricted. Therefore, even if not setting the total length or outside diameter of the writing instrument  1  large, the endcap  50  and clip  60  can be attached to the cap body  40  with sufficient mounting strength compared with for example the case of being received at the mount  12  only at the inside circumferential surface of the endcap inner cylinder  22 . 
     Note that, in the above assembly method, first, the endcap  50  may be fastened by insertion into the front end of the cap body  40 , then the insertion end part  61  of the clip  60  may be press-fit into the through hole  51  of the endcap  50  to fasten the clip  60  to the endcap  50  and cap body  40 . 
     The present invention can also be applied to writing instrument  1  which does not have a cap  2  instead of the above such writing instrument  1 . In this case, the back shaft  9  is formed with structures similar to the above-mentioned cylinder  11  and mount  12 . The endcap  5 ,  50  is attached to the open end formed at the back end of the back shaft  9 , that is, the cylinder  11 . The endcap  5  may be provided with the above-mentioned clip  6 ,  60  as well. In addition, the writing instrument  1  according to the present invention also includes, in addition to the above-mentioned water-based ink ball point pen, for example, a gel ink ball point pen, oil-based ink ball point pen, felt tip pen, or other writing instrument needless to say. 
     The present invention was explained based on specific embodiments, but a person skilled in the art could make various changes, corrections, etc. without departing from the claims and concept of the present invention. 
     REFERENCE SIGNS LIST 
     
         
           1  writing instrument 
           2  cap 
           3  writing instrument body 
           4 ,  40  body (cap body) 
           5 ,  50  endcap 
           6 ,  60  clip 
           11  cylinder 
           12  mount 
           18  air passage (inside air passage) 
           19  holding space 
           21  endcap outer cylinder 
           22  endcap inner cylinder 
           27  ring-shaped space (outside air passage) 
           28  cutaway part