254 



APPLIED SCIENCE 



When a bolt is less than an inch long, it is necessary to count the 

 grooves in H in. and multiply this by 2 to get the threads per inch. 

 The best way to measure threads is with the thread or pitch gauge. 



The number of 

 threads per inch is 

 the same on the 

 same sized bolt 

 whether the thread 

 is cut single, double, 

 or triple. If a double 

 thread, 8 threads 

 per inch is wanted, 

 we ask for "8 



. ,, threads per inch 



FIG. 115. Measurement of Screw Threads. , ,,,,., -. . , 



double | if a triple 



thread, we say "8 threads per inch triple." Although to avoid 

 any misunderstanding it would be clearer to say for the double 

 thread, " 34 in. lead, % in. pitch, double thread." There would 

 then be no chance for mistake since we sometimes find an old print 

 which calls for "8 threads per inch double," and means that 

 a double thread, 16 

 threads per inch is 

 wanted. With single 

 threads the word "sin- 

 gle " is not used, as it is 

 understood. All single 

 threads of coarse pitch 

 weaken considerably 

 the bolt or piece which 

 is threaded. For this 

 reason, multiple 

 threads are used. With 

 a double thread the 

 groove is only one-half 

 as deep as a corresponding single thread, and the bolt will ad- 

 vance just as far for one turn as it would if cut single. Figure 

 116 shows a triple thread with its corresponding single thread 

 dotted. 



FIG. 116. Triple-Thread Screw. 



