11 



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III. SCREWS, BOLTS, AND NUTS. 



Screw Threads. i :us forms of screw threads used 



in in < shown in tig. !). The H7//'/,r,,,-M V 



thread is shown at(a). This is the standard form of triangular 

 thread used in this country. The angle between th. 

 the V is 55, and one-sixth of the total depth is rounded off 

 both at the top and bottom. At (b) is shown the Seller* V 

 thread, which is the standard triangular thread uxrd 1,\ . 

 neers in America. In this form of thread the angle between tin 

 sides of the V is 60, and one-eighth of the total depth i 

 square off at the top and bottom. The Synnr'' thread is shown 

 at (r). This form is principally used for transmitting motion. 



(a) (b) (c) (d) <*> 





Comparing the triangular and square threads, the f.n 

 the stronger of the two ; but owing to the normal pressure on 

 the V thread being inclined to the axis of the screw, t In- 

 sure must be greater than the pressure which is ln-in^ tran> 

 mitted by the screw ; and therefore, seeing that the normal 

 pressure on the square thread is parallel, and therefore equal 

 to the pressure transmitted in the direction of the axis of the 

 screw, the friction of the V thread must be greater than the 



