ON THE SMALL SCREW GAUGE. 



385 



machines will have some rounding at the crests and roots o£ the threads,^ 

 we believe that we can secure the objects for which this Committee was 

 appointed in 1895, viz., to produce in a material form gauges which could 

 be checked by a central authority, such as the Board of Trade or the 

 National Physical Laboratory, and certified copies of which could be issued 

 to manufacturers and buyers of screws to secure commercial interchangs- 

 ability. 



We recommend, therefore, with reference to threads Nos. 0-11 : — 



1. That sets of gauges should be made and verified, each set consisting 

 of six pieces as follows, A-F. 



A. A male gauge screw of the pitch and effective diameter laid down 

 for the distinguishing number in Schedule I., the thread having a V-shaped 



Fig. 3. 

 Body of Nut 



Body of Screiv 



root, and a crest flattened cylindrically to the over-all diameter laid down 

 in the table. The outline of the thread is in fig. 3, A C F K M P S U. 



This piece A is for the purpose of testing nuts and nut gauges to check 

 the correctness of the pitch, angle of thread, effective diameter, and root < 

 diameter, and for checking the hole gauge E. ; 



B. A tap, a copy of A in all respects, except that it is fluted and 

 backed off as a tap, and that the crests are left nearly approaching the 

 sharp V form as is possible, so as to maintain a cutting edtje with this 

 angle of thread, i.e. 47-5 degs. The outline of this thread "is in tie. 3. 

 ABFLPTU. 



This piece B is to be used solely for cutting the tliread of the nut 

 gauge C. 



0. A nut gauge, the thread of which is cut by the tap B, the crest 

 being afterwards reamered out to such a diameter as experience may show 

 is necessary to give suitable minimum clearance at this point to ensure 



1903. e. c 



