252 



APPLIED SCIENCE 



295. Bolts. A bolt (Fig. 112) is a special form of screw 

 with a nut attached or screwed on the end to hold it in place. 

 A bolt can be more easily removed than a screw. Many 



machine shops, especially rail- 

 road shops, require a large 

 number of more or less ac- 

 curately threaded bolts. Bolt 

 machines thread these bolts by 

 means of a revolving die which 

 may be opened at the desired 

 place, permitting the quick 

 withdrawal of the bolt. 



(a) Round (&) Flat (c) Fillis- 296. Parts of Screw 



Head Head ter Head Threa d.-Certain definitions 



FIG. 112. Bolts. 



in regard to the screw should 



be carefully noted. A screw may be either right-handed or 

 left-handed. Right-handed means that, when turning it into 

 a nut or threaded hole the screw must be turned in the same 



direction as the hands _,, ^i 



^^> 



of a clock. When the 

 thread inclines or slopes 

 so that the under side is 

 nearer the right hand, it 

 is right-handed. 



The thread shown in 

 Fig. 1 13 is a single thread. FlG " "Swingle-Thread Screw. 

 Figure 114 shows a double thread. If three threads are wound 

 around the cylinder it would have a triple thread. Four or 

 five threads are sometimes wound around the cylinder, but 

 this type is not often found in shop practice. 



The distance from the bottom of one groove to the bottom 



