Abstract:
The present invention is a chuck body ( 13 ) provided with: a hollow, substantially cylindrical fastener ( 11 ) having a tapered inner surface ( 13 ) in which the diameter of the hole gradually changes along the axial direction; and a chuck ( 21 ) having a divided end part ( 23 ) divided into two or three, the divided end part ( 23 ) having a tapered outer surface ( 24 ) that can enter or exit from the fastener ( 11 ) and that comes into contact with the tapered inner surface ( 13 ) of the fastener ( 11 ) when entering the fastener ( 11 ). When the divided end part ( 23 ) of the chuck ( 21 ) closes in the fastener ( 11 ) and holds the core ( 10 ), the angle of the tapered outer surface ( 24 ) of the chuck ( 21 ) relative to the center axis line of the chuck ( 21 ) is substantially identical to the angle of the tapered inner surface ( 13 ) of the fastener ( 11 ).

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a National Stage application of PCT/JP2013/083224, filed Dec. 11, 2013, which claims priority from Japanese application JP 2012-270592, filed Dec. 11, 2012. 
     TECHNICAL FIELD 
     The present invention relates to a chuck member for feeding out and holding lead of a mechanical pencil. Furthermore, the present invention relates to a mechanical pencil which is provided with the chuck member. 
     BACKGROUND ART 
     To feed out and hold the lead of a mechanical pencil, in the past, a chuck member has been used. As shown in Japanese Patent Publication No. 2002-321493A, the chuck member is comprised of a chuck and a fastener (fastening ring). The fastener is a hollow substantially cylindrical shape and has a straight inner circumference in the axial line direction. The chuck is split at one end part in the longitudinal direction. The split end part of this chuck enables insertion and withdrawal to and from the fastener and has a tapered outer surface which contacts the inner surface of the fastener when inserted in the fastener. As shown in Japanese Patent Publication No. 2012-158092A, the material of the chuck is typically a metal or plastic. 
     If the biasing force of a spring causes a chuck to enter a fastener, the tapered outer surface of the chuck receives drag from the inner surface of the fastener, so the split end part of the chuck closes and holds the lead. At the time of writing, in addition to the biasing force of the spring, writing pressure is applied to the chuck through the lead, so the tapered outer surface of the chuck receives a further stronger drag from the inner surface of the fastener. For this reason, the lead is held by the chuck by a stronger holding force, so at the time of writing, the lead can be prevented from sliding back. Note that it is known that a similar advantageous effect can be obtained even by a configuration where the fastener has a tapered inner surface and the chuck has a straight outer surface. 
     SUMMARY OF INVENTION 
     Technical Problem 
     However, even in a state where the lead is held by the chuck, at the time of start of writing, the writing pressure causes the chuck to be pushed into the fastener together with the lead resulting in the lead sliding back into the tip. The amount of slide back is slight, but sometimes it causes an odd sensation of use to the user. For this reason, it is preferable to make the amount of slide back of the lead as close to zero as possible. Further, if an extremely strong writing pressure is applied to the lead, the lead which is held by the chuck slides with respect to the chuck making writing impossible. Furthermore as explained later in the explanation of the present invention, the force of the chuck holding the lead becomes local, so the lead sometimes fractures. This phenomenon may be called “biteoff” of the lead. 
     The amount of slide back, the holding ability, and the fracture resistance of the lead of the chuck member depend on the material and size of the chuck. A high rigidity metal chuck is known to have a smaller amount of slide back of the lead than a plastic chuck and to have a higher holding ability and fracture resistance of the lead than a plastic chuck. However, a metal chuck is more expensive in terms of cost of materials and cost of processing than a plastic chuck. For this reason, when using a metal chuck, it is difficult to provide an inexpensive mechanical pencil. 
     Further, it is also known that by enlarging the split end part of a plastic chuck which holds the lead, the amount of slide back, holding ability, and fracture resistance of the lead of a plastic chuck approaches the amount of slide back, holding ability, and fracture resistance of the lead of a metal chuck. However, a plastic chuck with a large outer shape cannot be used for a mechanical pencil with a multicolor mechanical refill or fine lead. 
     Therefore, the present invention has as its object the provision of a chuck member which, regardless of the material or size of the chuck, enables small slide back of the lead and high lead holding ability and fracture resistance. 
     Solution to Problem 
     In a first aspect of the present invention, there is provided a chuck member comprising a hollow substantially cylindrical shape fastener which has a tapered inner surface where a diameter of its hole gradually changes in an axial line direction and a chuck which has a split end part which is split into two or three sections, the split end part being able to be inserted into and withdrawn from the fastener and having a tapered outer surface which contacts the tapered inner surface of the fastener when entering into the fastener, wherein, when the split end part of the chuck closes inside the fastener and holds the lead, the angle of the tapered output surface of the check is equal to the angle of the tapered inner surface of the fastener with respect to the center axial line of the chuck. Note that “when the split end part of the chuck closes inside the fastener and holds the lead” means the state where the lead does not drop out of the chuck due to gravity when the axial line direction of the lead matches with the direction of gravity. 
     In the first aspect of the present invention, preferably the chuck is comprised of a plastic which has elasticity. 
     In the first aspect of the present invention, preferably the invention is configured so that both end parts of the tapered inner surface of the fastener in the axial line direction do not contact the tapered outer surface of the chuck. 
     In the first aspect of the present invention, preferably the invention is configured so that the both end parts of the fastener are away from the tapered outer surface of the chuck in the radial direction. 
     In a second aspect of the present invention, there is provided a mechanical pencil which is provided with a chuck member of one aspect of the present invention. 
     Advantageous Effects of Invention 
     According to the present invention, a chuck member which, regardless of the material or size of the chuck, enables small slide back of the lead and high lead holding ability and fracture resistance is provided. 
     Below, the present invention will be much more sufficiently 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 cross-sectional view of a mechanical pencil according to the present invention. 
         FIG. 2  is a side cross-sectional view of a mechanical pencil according to the present invention. 
         FIG. 3  is an enlarged perspective view of a chuck member according to the present invention. 
         FIG. 4  is a side view of a chuck according to the present invention. 
         FIG. 5  is a side cross-sectional view of a chuck member according to the present invention. 
         FIG. 6  is a partial side cross-sectional view of a chuck member according to the prior art. 
         FIG. 7  is a partial side cross-sectional view of a chuck member according to the present invention. 
         FIG. 8  is a partial side cross-sectional view of a chuck member according to the prior art. 
         FIG. 9  is a graph which shows the results of a lead holding ability test. 
         FIG. 10  is a graph which shows the results of a lead fracture resistance test. 
         FIG. 11  is a graph which shows the results of a lead slide back amount test. 
         FIG. 12  is a partial side cross-sectional view of a chuck member when holding lead with a large lead diameter. 
         FIG. 13  is a partial side cross-sectional view of a chuck member when holding lead with a small lead diameter. 
         FIG. 14  is a partial side cross-sectional view of a chuck member according to another embodiment of the present invention. 
         FIG. 15  is a partial side cross-sectional view of a chuck member according to still another embodiment of the present invention. 
         FIG. 16  is a partial side cross-sectional view of a chuck member according to still another embodiment of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Below, referring to the attached drawings, the present invention will be explained. Further, in the attached drawings, the same components are assigned the same reference notations. 
     First, referring to  FIG. 1  and  FIG. 2 , the setup by which lead  10  is fed out in the mechanical pencil  1  will be simply explained. 
       FIG. 1  and  FIG. 2  are side cross-sectional views of a mechanical pencil  1  according to the present invention. The mechanical pencil  1  is comprised of, as the configuration for feeding out the lead  10 , a click part  2 , lead case  3 , fastener  11 , chuck  21 , spring  4 , and holding member  5 . The click part  2  engages with the lead case  3 . The chuck  21  has, in the longitudinal direction, an engagement end part  22  which is engaged with the lead case  3  and a split end part  23  which can be inserted into and withdrawn from the fastener  11 . As shown in  FIG. 4 , the chuck is configured so that if the split end part  23  of the chuck  21  leaves the fastener  11 , it opens. The fastener  11  is housed slidably inside the tube  6 . 
       FIG. 1  and  FIG. 2  differ in the positions of the fastener  11  and chuck  21  inside the mechanical pencil. In  FIG. 1 , the click part  2  is not pushed. When the click part  2  is not pushed, the chuck  21  is biased by the spring  4  to the click part  2  side through the lead case  3 . That is, the split end part  23  of the chuck  21  is fastened inside of the fastener  11 . At this time, the outer surface of the split end part  23  of the chuck  21  and the inner surface of the fastener  11  have complementary tapered shapes, so the split end part  23  of the chuck  21  receives drag from the fastener  11  and closes. For this reason, the lead  10  is held by the chuck  21 . 
     On the other hand, as shown in  FIG. 2 , if the click part  2  is pushed, the pushing force is transmitted through the lead case  3  to the chuck  21 . If the pushing force is larger than the biasing force of the spring  4 , the chuck  21  advances together with the lead  10  and fastener  11 . If the split end part  23  of the chuck  21  sticks out from the fastener  11 , the split end part  23  opens, so the lead  10  is released from the chuck  21 . At this time, the lead  10  is held by the holding member  5 . After that, if the click part  2  is released, the split end part  23  of the chuck  21  enters into the fastener  11  again due to the biasing force of the spring  4 , but the lead  10  is held by the holding member  5 , so does not retract. By repeatedly pushing the click part  2 , the lead  10  is successively fed out from the tip. In this way, the chuck  21  works with the fastener  11  to feed out and hold the lead  10 . Note that, as shown in  FIG. 1  and  FIG. 2 , in the Description, the front end of the mechanical pencil  1 , that is, the tip side, is defined as the “front” side of the mechanical pencil  1 , while the side opposite to the tip of the mechanical pencil  1  along the longitudinal direction of the mechanical pencil  1  is defined as the “back” side of the mechanical pencil  1 . 
     Next, the chuck member  31  according to the present invention will be explained in detail. The chuck member  31  is comprised of a chuck  21  and a fastener  11 . 
       FIG. 3  is an enlarged perspective view of the chuck member  31  according to the present invention. The fastener  11  has a hollow substantially cylindrical shape. The material of the fastener  11  is typically brass. 
       FIG. 4  is a side view of a chuck  21  according to the present invention. As shown in  FIG. 4 , the chuck  21  has one end part  23  in the longitudinal direction split into two symmetrically in the radial direction. This split end part  23  of the chuck  21  can be inserted into and withdrawn from the fastener  11  and has a tapered outer surface  24  which contacts the inner surface of the fastener  11  when it enters the fastener  11 . The angle α of the tapered outer surface  24  with respect to the axial line of the chuck  21  gradually decreases when the split end part  23  of the chuck  21  is fastened inside the fastener  11 . In  FIG. 3 , the split end part  23  of the chuck  21  closes inside the fastener  11  and holds the lead  10 . Note that the split end part  23  of the chuck  21  may also be split into three sections. 
       FIG. 5  is a side cross-sectional view of a chuck member  31  according to the present invention. As shown in  FIG. 5 , the fastener  11  has a tapered inner surface  13  where a diameter of its hole gradually changes in an axial line direction. More specifically, the fastener  11  has a diameter of its hole which gradually decreases in the axial line direction toward the back. The taper angle of this tapered inner surface  13  with respect to the center axial line of the fastener  11  is about 3°. Note that, as shown in  FIG. 5 , in the Description, the side of the lead  10  which is held by the chuck  21  is defined as the “front” side of the chuck member  31 , while the side opposite to the side of the lead  10  which is held by the chuck  21  along the longitudinal direction of the chuck member  31  is defined as the “back” side of the chuck member  31 . 
     As shown in  FIG. 5 , when the split end part  23  of the chuck  21  closes inside the fastener  11  to hold the lead  10 , the angle of the tapered outer surface  24  of the chuck  21  with respect to the center axial line of the chuck  21  becomes substantially equal to the angle of the tapered inner surface  13  of the fastener  11 . In other words, when the split end part  23  of the chuck  21  closes inside the fastener  11  and holds the lead  10 , the tapered outer surface  24  of the chuck  21  contacts the tapered inner surface  13  of the fastener  11  by a plane. Note that, as shown in  FIG. 5 , the center axial line of the chuck  21  and the center axial line of the fastener  11  are equal. Further, in this Description, “when the split end part  23  of the chuck  21  closes inside the fastener  11  and holds the lead  10 ” means the state where the lead  10  does not drop out of the chuck  21  due to gravity when the axial line direction of the lead  10  matches with the direction of gravity. 
     Below, a chuck member  31  according to the present invention will be explained in comparison with the prior art. 
       FIG. 6  is a partial side cross-sectional view of a chuck member  301  according to the prior art.  FIG. 7  is a partial side cross-sectional view of a chuck member  31  according to the present invention. The chuck members  301  and  31  have shapes which are symmetrical in the radial direction, so, for simplification, in  FIG. 6  and  FIG. 7 , only single sides of the chuck members  301  and  31  are shown. As shown in  FIG. 6 , the fastener  101  according to the prior art has an inner surface  103  which extends straight in the axial line direction. For this reason, when the chuck  201  holds the lead  10 , the tapered outer surface  240  of the chuck  201  contacts the inner surface  103  of the fastener  101  by a line. In this case, the contact area of the chuck  201  and the fastener  101  is small, so the chuck can easily be pushed in the fastener together with the lead and the amount of slide back of the lead becomes larger. Further, the tapered outer surface  240  of the chuck  201  locally deforms whereby deformation of the holding part  250  of the chuck  201  occurs, so the holding ability of the lead  10  becomes lower. Further, the drag from the fastener  101  is locally applied to the lead  10 , so the fracture resistance of the lead  10  becomes lower. Note that, as shown in  FIG. 8 , a similar inconvenience occurs in the case where the outer surface  204  of the chuck  202  extends straight in the axial line direction and the inner surface  104  of the fastener  102  is a tapered shape. 
     On the other hand, as shown in  FIG. 5  and  FIG. 7 , the fastener  11  according to the present invention has a tapered inner surface  13  where a diameter of its hole gradually decreases in an axial line direction toward the back. Further, the angle of the tapered outer surface  24  of the chuck  21  becomes substantially equal to the angle of the tapered inner surface  13  of the fastener  11  with respect to the center axial line of the chuck  21 . For this reason, when the chuck  21  holds the lead  10 , the tapered outer surface  24  of the chuck  21  contacts the tapered inner surface  13  of the fastener  11  by a plane. In this case, the contact area between the chuck  21  and the fastener  11  is large, so the chuck becomes hard to be pushed into the fastener together with the lead and the amount of slide back of the lead becomes small. Further, the drag from the inner surface of the fastener  11  is dispersed, so the local deformation of the tapered outer surface  24  of the chuck  21  is reduced and in turn the deformation of the holding part  25  of the chuck  21  is reduced. This raises the holding ability of the lead  10 . Furthermore, the drag from the inner surface  13  of the fastener  11  is applied evenly to the lead  10 , so the fracture resistance of the lead  10  is raised. 
     Below, the results of three tests relating to the lead holding ability, fracture resistance, and amount of slide back using chuck members according to the prior art and a chuck member according to the present invention are shown. In the tests, three types of chuck members according to the prior art and a chuck member according to the present invention, that is, a total of four types of samples, were used. An outline of the chucks of the chuck members which were used is shown in the following table. 
     
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Length L of 
                 Thickness of 
                   
               
               
                   
                 holding part 
                 holding part T 
               
               
                   
                 (mm) 
                 (mm) 
                 Material 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 Sample 1 (prior art) 
                 2.3 
                 1.0 
                 POM (GF25%) 
               
               
                 Sample 2 (prior art) 
                 3.5 
                 1.4 
                 POM 
               
               
                 Sample 3 (prior art) 
                 2.35 
                 0.9 
                 Brass 
               
               
                 Sample 4 (invention) 
                 2.3 
                 1.0 
                 POM 
               
               
                   
               
             
          
         
       
     
     The holding part length L and holding part thickness T are shown in  FIG. 5 . The chucks of Sample 1 and Sample 2 were plastic (polyacetal (POM)) chucks according to the prior art. The chucks and fasteners were shaped as shown in  FIG. 6 . Note that the material of the chuck of Sample 1, that is, POM, contained glass fiber to 25%. Sample 3 was a metal (brass) chuck according to the prior art. The chuck and fastener were shaped as shown in  FIG. 8 . Sample 4 was a plastic (polyacetal) chuck according to the present invention. The chuck and fastener were shaped as shown in  FIG. 7 . The chucks of Samples 1, 3, and 4 had equal sizes, while the plastic chuck of Sample 2 was larger than the other chucks. 
     Lead Holding Ability Test 
     In this test, the lead which was fed out from the tip was pushed against a platform scale and the load (holding force) beyond which the lead slid out from the chuck was measured. The measurement was conducted for each number of clicks.  FIG. 9  is a graph which shows the result of the lead holding ability test. In the chuck member according to the prior art (Sample 1), with a less than 20N holding force, the lead slid out from the chuck. As the number of clicks increased, the holding force beyond which the lead slid out fell. In the other chuck members (Samples 2 to 4), regardless of the number of clicks, the lead did not slide out from the chuck with a 25N holding force. From this result, it was proved that the chuck member according to the present invention (Sample 4) has a high lead holding ability regardless of being a plastic chuck of a small chuck size. Note that, the holding force (N) of the ordinate of the graph of  FIG. 9  expresses the load on the chuck due only to the writing pressure and does not include the biasing force of the spring. Therefore, in actuality, the chucks were subjected to a load of the holding force plus the biasing force of the spring (about 5N). 
     Lead Fracture Resistance Test 
     In this test, the load (holding force) when the chuck which is inserted into the fastener was pulled backward and the lead fractured was measured.  FIG. 10  is a graph which shows the results of the lead fracture resistance test. In the chuck member according to the prior art (Sample 1), the lead fractured with a 20N holding force. In the other chuck members (Samples 2 to 4), the lead did not fracture even with a 30N holding force. From this result, it was proved that the chuck member according to the present invention (Sample 4), despite the chuck being a small plastic chuck, has a high lead fracture resistance. 
     Lead Slide Back Amount Test 
     In this test, the chuck which is inserted into the fastener was pulled backward and the engagement position was measured for each load (holding force). The “engagement position” is the distance from the front end of the chuck to the front end of the fastener and is shown by the notation D in  FIG. 5 . The engagement position at the time of a 5N load, corresponding to the biasing force of the spring against the chuck, was used as a reference value and the difference between the reference value and the engagement position for each load was made the amount of slide back of the lead. Slide back of the lead occurs due to the the chuck which holds the lead sliding back with respect to the fastener.  FIG. 11  is a graph which shows the results of the lead slide back test. The amount of slide back of the lead of the chuck member according to the present invention (Sample 4) was smaller than the amounts of slide back of the leads of the chuck members according to the prior art (Samples 1 and 2). From this result, it was proved that the chuck member according to the present invention (Sample 4), despite the chuck being a small plastic chuck, has a small lead slide back amount. 
     In this regard, the size of the commercially available lead which is used (lead diameter) is not always constant. Typically, the lead diameter varies by ±0.02 mm. When the lead diameter is smaller or larger than the reference value, the angle of the tapered outer surface  24  of the chuck  11  with respect to the center axial line of the chuck  11  deviates from the angle of the tapered inner surface  13  of the fastener  11  when the split end part  23  of the chuck  21  closes to hold the lead  10 .  FIG. 12  is a partial side cross-sectional view of a chuck member  31  when a lead  20  of a large lead diameter is held.  FIG. 13  is a partial side cross-sectional view of a chuck member  31  when a lead  20  of a small lead diameter is held. For simplification, in  FIG. 12  and  FIG. 13 , only one side of the chuck member  31  is shown. 
     As shown in  FIG. 12 , when the lead diameter is large, the back part of the split end part  23  of the chuck  21  contacts the lead  20  while the front part of the tapered outer surface  24  of the chuck  21  contacts the tapered inner surface  13  of the fastener  11 . At this time, the angle of the tapered outer surface  24  of the chuck  21  deviates from the angle of the tapered inner surface  13  of the fastener  11  with respect to the center axial line of the chuck  21 . In other words, the tapered outer surface  24  of the chuck  21  contacts the tapered inner surface  13  of the fastener  11  by a line. On the other hand, as shown in  FIG. 13 , when the lead diameter is small, the front part of the split end part  23  of the chuck  21  contacts the lead  30  while the back part of the tapered outer surface  24  of the chuck  21  contacts the tapered inner surface  13  of the fastener  11 . At this time, the angle of the tapered outer surface  24  of the chuck  21  deviates from the angle of the tapered inner surface  13  of the fastener  11  with respect to the center axial line of the chuck  21 . In other words, the tapered outer surface  24  of the chuck  21  contacts the tapered inner surface  13  of the fastener  11  by a line. However, this inconvenience is solved by the features of the present invention which are explained below. 
     The chuck  21  according to the present invention is comprised of a plastic which has elasticity. The “plastic which has elasticity” is, for example, polyacetal, nylon, polypropylene, polyethylene, etc. Due to this, both when the lead diameter is large or small, the chuck  21  will suitably deform to match with the fastener  11 , so when the split end part  23  of the chuck  21  closes to hold the lead  10 , the angle of the tapered outer surface  24  of the chuck  21  becomes substantially equal to the angle of the tapered inner surface  13  of the fastener  11  with respect to the center axial line of the chuck  21 . Therefore, according to the chuck member  31  according to the present invention, regardless of variations in the lead diameter, a small amount of slide back of the lead and a high lead holding ability and fracture resistance can be obtained. 
     However, if the chuck  21  has elasticity, the edges of the both end parts of the tapered inner surface  13  of the fastener  11  in the axial line direction catch on the tapered outer surface  24  of the chuck  21  and result in poor fastening of the chuck  21  in some cases. This inconvenience is solved by the following configuration of the present invention. 
       FIG. 14  is a partial side cross-sectional view of a chuck member  32  according to another embodiment of the present invention. For simplification, in  FIG. 14 , only one side of the chuck member  32  is shown. This embodiment is configured so that the both end parts (front end part  15  and rear end part  16 ) of the tapered inner surface  14  of the fastener  12  in the axial line direction are away from the tapered outer surface  24  of the chuck  21  in the radial direction. More specifically, as shown in  FIG. 14 , the both end parts  15  and  16  of the tapered inner surface  14  of the fastener  12  in the axial line direction are chamfered to a tapered shape so as to be away from the tapered outer surface  24  of the chuck  21  in the radial direction. This chamfered shape may also be a rounded shape. Due to this configuration, the edges of the both end parts  15  and  16  of the fastener  12  are prevented from catching on the tapered outer surface  24  of the chuck  21  and in turn poor fastening of the chuck  21  is prevented. 
       FIG. 15  is a partial side cross-sectional view of a chuck member  33  according to still another embodiment of the present invention. For simplification, in  FIG. 15 , only one side of the chuck member  33  is shown. This embodiment is configured so that the rear end part of the tapered outer surface  26  of the chuck  51  is away from the tapered inner surface  43  of the fastener  41  in the radial direction. Further, as shown in  FIG. 15 , the front end part  45  of the axial line direction of the tapered inner surface  43  of the fastener  41  is chamfered to a tapered shape so as to be away from the tapered outer surface  26  of the chuck  51  in the radial direction. This chamfered shape may be a rounded shape as well. Due to this configuration, the edges of the both end parts (front end part  45  and rear end part  46 ) of the fastener  41  are prevented from catching on the tapered outer surface  26  of the chuck  51  and in turn poor fastening of the chuck  51  is prevented. 
       FIG. 16  is a partial side cross-sectional view of a chuck member  34  according to still another embodiment of the present invention. For simplification, in  FIG. 16 , only one side of the chuck member  34  is shown. In this embodiment, at the time of fastening, to prevent the rear end part of the tapered outer surface  27  of the chuck  52  from contacting the edges of the rear end part  48  of the tapered inner surface  44  of the fastener  42 , the length of the fastener  42  in the axial line direction is made longer. Further, as shown in  FIG. 16 , the front end part  47  of the tapered inner surface  44  of the fastener  42  in the axial line direction is chamfered to a tapered shape so as to be away from the tapered outer surface  27  of the chuck  52  in the radial direction. This chamfered shape may also be a rounded shape. Due to this configuration, the edges of the both end parts  47 ,  48  of the fastener  42  are prevented from catching on the tapered outer surface  27  of the chuck  52  and in turn poor fastening of the chuck  52  is prevented. 
     Above, several preferred embodiments according to the present invention were explained, but the present invention is not limited to these embodiments. Various modifications and changes may be made within the scope of the claims. For example, the chuck may be not a plastic chuck, but a metal chuck. Further, the embodiments may be combined with each other. 
     REFERENCE SIGNS LIST 
     
         
           1  mechanical pencil 
           2  click part 
           3  lead case 
           4  spring 
           5  holding member 
           6  tube 
           10 ,  20 ,  30  lead 
           11 ,  12 ,  41 ,  42 ,  101 ,  102  fastener 
           13 ,  14 ,  43 ,  44  tapered inner surface 
           15 ,  45 ,  47  front end part 
           16 ,  46 ,  48  rear end part 
           21 ,  51 ,  52 ,  201 ,  202  chuck 
           22  engagement end part 
           23  split end part 
           24 ,  26 ,  27 ,  240  tapered outer surface 
           25 ,  250  holding part 
           31 ,  32 ,  33 ,  34 ,  301 ,  302  chuck member 
           103 ,  104  inner surface of fastener 
           204  outer surface of chuck