ON THE SCREW GAUGE. 531 
gauges are available for immediate comparison, and where the photographic 
and microscopic methods can be readily applied to verify gauges and to 
obtain a record of those submitted for examination. This means work 
to be done, expenses to be incurred, and fees to be paid, as is now done at 
the Kew Observatory for chronometers, thermometers, &e. 
Ill. Tue Furure. 
The opinions formed by the Committee, after full and exhaustive dis- 
cussions, for furthering the objects to be attained may be summarised as 
follows :— 
(a) The Committee recommend the construction and housing of the comb 
form of gauges or templates of the B.A. screw thread, by comparison with 
which master gauges or templates may be exactly and conveniently verified. 
(6) That, as no exact system of testing femaie threads has yet been 
devised, the Committee restrict themselves to recommending means for 
keeping male threads to gauge, and this they consider will be sufficient 
for the purpose of securing practical uniformity in female screws. 
(c) Male threads can best be measured by the comb, combined with 
suitably arranged tests to give the correct diameters. 
(d) That for purposes of verification or standardisation the gauges to 
be deposited for reference should consist of a complete set of these comb- 
pieces, and a complete corresponding set of male screws, so that new 
combs can be compared with those deposited, or male screws can be com- 
pared with the standard combs with great accuracy by the photographic 
or the microscopic method, and that these two methods may be conve- 
niently used to check and corroborate each other. 
(e) That in order to obtain interchangeability of these male screws for 
practical workshop use it is sufficient that they should satisfy the following 
tests :— ; 
(1) There should be no appreciable difference in the fit of the screw 
with a standard comb having not less than twelve teeth. 
(2) The diameter of the core must not exceed that laid down by the 
B.A. specification. 
(3) The diameter of the screw measured over the thread must not ex- 
ceed that laid down by the B.A. specification. 
4) The diameter of the screw measured over the thread must not fall 
short of that laid down by the B.A. specification by more than a certain 
amount, which amount depends on the class of work and purpose to which 
the screw is to be applied. 
The amount referred to in (4) must be settled by the persons in con- 
‘trol of the work for which the screws are to be used. 
(f) They recommend for general use in the workshop the half-nut 
gauge, as described in Appendix II., combined with inside and outside 
diameter gauges. 
The Committee, in printing the tables, Appendix III., for which they 
have to thank Mr. Le Neve Foster and Mr. Price, do not take the respon- 
sibility of recommending any limits, but publish the information as an 
indication of the limits of accuracy within which these screws may be 
expected to be produced in practice. 
If the recommendations of the Committee be approved of, they further 
recommend that the Committee should be reappointed for the purpose of 
obtaining and verifying standard combs and male screws, and determining 
the future home of the gauges. 
MM2 
