COMMON FASTENING AGENTS 255 



298. Depth of Thread. It is important to be able to 

 find the depth of a thread, for upon this depends the cutting 

 of all threads and the size of all tap drills. By referring to 

 Fig. 117, we see that the depth of the thread is the altitude 

 of a right-angle triangle, since the angles are all 60 and the 

 sides of the V or groove are equal ^._. PITCH ^ 



to the pitch. Knowing two sides /K /JO ^ 



of a right-angle triangle we can A^oA /jj V ^ 

 easily find the other, since we /%. \/ 5j \\x 

 know that the square of the alti- " JIL./^ .Zj| 



tude of any right-angle triangle is FIG. 117. Measurement of 

 equal to the square of the hypo- pitch of Screw - 



tenuse minus the square of the third side. A simple problem in 

 square root will give the correct figure for the altitude of depth. 

 An easier way to find the depth of a United States or V 

 thread is to remember that the depth of a United States 

 thread of 1 in. pitch is .65 in. and the depth of a V thread of 

 1 in. pitch is .86 in. Now if we wish to find the depth 

 of any other thread we simply divide these figures by the 

 number of threads to the inch. For example, we determine 

 the depth of a United States standard thread 13 threads to 

 the inch in this manner .65 + 13 = .05 in., and the depth 

 of a V thread 4 threads per inch, in this manner .86 -=- 4 

 = .215. When figuring the size to bore or drill a nut or 

 a hole to be threaded, subtract the double depth of the thread 

 from the outside diameter of the thread on the bolt or 

 rod. 



299. Kinds of Screw Threads. There are many kinds of 

 bolts and screws to meet different needs and in order to 

 specify a particular grade of bolt or screw it is necessary to 

 mention : 



