ON THE SMALL SCREW CtAUGE. 



381 



For the convenience of English measurement, the nearest equivalents 

 of the pitches and diametei's of screws in thousandths of an inch are given 

 in Schedule III. 



Schedule III. — Schedule of approximate dimensions in thousandths 



of an inch. 



In practice interchangeability has been to some extent secured by- 

 allowing clearances at the root and crest of the thread. The Committee 

 think it desirable to suggest the amount of these clearances in the gauges, 

 and they have agreed : 



(a) That clearance should be provided at the root of the thread of the 

 screws, and should be obtained by cutting the thread of the screw deeper 

 than the normal, thereby reducing the diameter of the core ; 



(b) That clearance may be provided at the crest of the thi-ead of the 

 screw, and should be obtained by the use of a tap whose outside diameter 

 is greater tlian the normal ; 



(c) That the limits of these clearances be defined by the figures of 

 Schedule IT. 



