Bolt & Nut

Abstract

A bolt and nut can be smoothly engages with a mating nut and a mating bolt, respectively, even if the threads of the mating nut and the mating bolt have metal particles or paint particles sticking thereto. The bolt has a regularly threaded part ( 3 ) capable of being regularly engaged with the mating nut, and a cylindrical guide part ( 4 ) extending from the regularly threaded part and having a diameter smaller than the minor diameter of the internal thread of the mating nut. A slot ( 5 ) is formed in the end surface of the cylindrical guide part.

1 . A bolt having: 
 a regularly threaded part provided with a regular external thread capable of being regularly engaged with an internal thread formed in a mating nut; and    a cylindrical guide part having a diameter smaller than a minor diameter of the internal thread of the mating nut and contiguous with the regularly threaded part;    wherein the cylindrical guide part is provided with a recess in its end surface.    
   
   
       2 . The bolt according to  claim 1 , wherein the recess is formed by axially cutting an end part of the cylindrical guide part.  
   
   
       3 . The bolt according to  claim 1 , wherein longitudinal grooves are formed in a circumference of the cylindrical guide part.  
   
   
       4 . The bolt according to  claim 1 , wherein the regularly threaded part is provided with grooves having a length corresponding to at least one screw thread of the regular external thread and formed in a portion thereof contiguous with the cylindrical guide part.  
   
   
       5 . The bolt according to  claim 4 , wherein the grooves are formed in a length corresponding to one to three screw threads of the regular external thread in a portion of the regularly threaded part contiguous with the cylindrical guide part.  
   
   
       6 . A nut provided with a threaded bore having an internal thread that can be engaged with an external thread of a mating externally threaded member; 
 wherein the threaded bore has a leading part that is engaged first with the external thread of the mating externally threaded member, provided with a plurality of recesses having a length equal to at least one pitch of the internal thread and arranged at equal angular intervals, and a regularly threaded part capable of being engaged with the external thread of the mating externally threaded member and continuous with the leading part.    
   
   
       7 . The nut according to  claim 6 , wherein a sum of circumferential lengths of the recesses is not shorter than half a circumferential length of the regularly threaded part.  
   
   
       8 . The nut according to  claim 6 , wherein a radial depth of the recesses is in the range of a value equal to a height of the internal thread of the regularly threaded part and a value twice the height of the internal thread of the regularly threaded part.  
   
   
       9 . The nut according to  claim 6 , wherein an axial length of the recesses formed in the leading section of the threaded bore is equal to one to two pitches of the internal thread.  
   
   
       10 . A bolt having: 
 a head against which a fastening tool is pressed to screw the bolt in a threaded bore of a mating nut provided with an internal thread;    a cylindrical guide part of a diameter smaller than a minor diameter of the internal thread of the nut;    a regularly threaded part that engages regularly with the internal thread of the nut; and    a threaded guide part formed between the cylindrical guide part and the regularly threaded part, provided with an external thread having rounded crests and having a major diameter greater than the diameter of the cylindrical guide part and smaller than a major diameter of the external thread of the regularly threaded part.    
   
   
       11 . The bolt according to  claim 10 , wherein the external thread of the threaded guide part is the same in pitch and lead angle as that of the regularly threaded part.  
   
   
       12 . The bolt according to  claim 10 , wherein the external thread of the threaded guide part has a screw thread form that can be included in a screw thread form of the external thread of the regularly threaded part when the former is superposed on the latter.  
   
   
       13 . The major diameter of the external thread of the threaded guide part at a position on the axis nearer to the head of the bolt is greater than that of the same at a position on the axis nearer to the extremity of the bolt, and the external thread of the threaded guide part has at least two major diameters.  
   
   
       14 . The bolt according to  claim 10 , wherein the external thread of the threaded guide part has a single major diameter.  
   
   
       15 . The bolt according to  claim 10 , wherein a radius of curvature of rounded crests of the external thread of the threaded guide part in a screw thread form is in the range of 20% to 60% of the pitch.  
   
   
       16 . The bolt according to  claim 10 , an edge of an end surface of the cylindrical guide part is rounded in a radius of curvature equal to 50% of the pitch or above.