256 APPLIED SCIENCE 



(a) Shape or form of thread. 



(b) Pitch, or number of threads to the inch. 



(c) Shape of head. 



(d) Outline of body, barrel, or stem. 



(e) Diameter. 



(/) Direction of thread. 



(g) Length. 



(h) Material. 



Before 1861 every manufacturer had a peculiar thread 

 that he made for his own work. The result was that the 

 large number of threads caused confusion among engineers 

 and machinists. To avoid this it was proposed to have a 

 standard form; today each country has a standard of its own. 



300. Standard Threads. The two forms of screw threads 

 in use in the United States are the common V thread and 

 the United States standard thread, while the Whitworth screw 

 is the most common in England. 



The V-shaped thread (Fig. 118a) is a thread having its 

 sides at an angle of 60 to each other and perfectly sharp 



at the top and bottom. 

 This thread is used most- 

 ly on screws designed for 



(a)VThread (6) Whit- fr) United ^-working and for 

 worth States small brass work. The 



Thread Standard objections to its use are 



FIG. 118. Standard Screw Threads. , J 



that the top, being very 



sharp, is injured by the slightest accident; and that in the use 

 of taps and dies, the fine, sharp edge is quickly lost, causing 

 constant variation in fitting. 



The V-shaped thread is the strongest form of screw thread 

 used in the making of bolts. But because the thrust be- 



