mem 
ON THE SCREW GAUGE. 53D 
sizes for B.A. screws. A screw should pass into this hole freely, but 
without much shake. The hole é is the minimum gauge, and the screw 
should not pass into this hole. The difference of diameter between the 
holes a and 6 has not yet been determined by the Committee ; in the 
present case it is 0015 in. ¢ is a threaded hole or female gauge in which 
a screw should just turn freely. The hole d is for the diameter of the 
core, but as it is impossible, without turning down some of the threads 
of a screw, to pass the core of it into this hole, the gauge e is provided 
for gauging the core, or, in other words, the depth of the thread. It 
consists of a fork the inner edges of which are shaped so as to enter 
between the threads of a screw. The correctness of the pitch of a screw 
is ascertained by placing it in the comb / and against the back-rest g, and 
by holding the gauge against the light or a white paper. 
It has been found by practice that there is considerable difficulty in 
making these combs with any degree of accuracy, and also that it would 
be almost impossible to carry out the above form of gauge for the smaller 
sizes. It is therefore suggested that the gauge represented in fig. 5 has 
certain advantages over the comb-gauge. With this the half-nut h is 
employed for verifying the pitch of screws instead of the comb. The 
half-nut can be carried out with greater certainty and ease, and is there- 
fore less costly, and there is no difficulty in making it for the smaller 
sizes, as shown in fig. 6. Gauges on the principle of figs. 5 and 6 have 
also the advantage of being more compact and stronger for workshop 
use. 
The process of making the half-nut gauges is the following :—Two 
have to be made at one time. When the two steel bars intended for 
the gauges are filed to shape they are placed together, as shown in sketch 
