~ ote san 
ON THE SMALL SCREW GAUGE. 465 
the Committee have been in communication with different firms, and 
principally with the Pratt and Whitney Company of Hartford, U.S.A., a 
firm enjoying the very highest reputation for work of the kind the 
Committee desired to secure. Finding that this firm were prepared to 
undertake the production of gauges and tools for the British Association 
screw-threads on the same lines as they have adopted with the American 
and Whitworth threads, the Committee have been satisfied to leave the 
matter in the hands of the Company till they should ascertain whether 
they could produce the desired result, and have given them all the 
information, specifications, &c., that were possible. Within the last two 
months the Pratt and Whitney Company have submitted to the Committee 
specimens in hard steel of male and female gauge pieces of threads Nos. 3, 
7,and 13. The three male screws of these sets have been photographed 
by Colonel Watkin on a large scale, and have been measured by Mr. 
H. J. Chaney, Superintendent of the Standards Department of the Board 
of Trade. Their two reports are printed below. 
The Committee believe these gauges to be sufticiently accurate for 
practical requirements. The material of which they are made—hardened 
steel—should enable them to stand much use without injury. Their finish 
and general workmanship are exceedingly good. 
The Committee, through their Secretary, have expressed to the Pratt 
and Whitney Company their satisfaction with these gauges, and have 
been informed in reply that a higher degree of accuracy may be expected 
in the future. They are still in correspondence respecting the specifica- 
tions of limits of error and other details concerning their production on 
the commercial scale. The manufacture and ‘sale of these gauges by the 
Pratt and Whitney Company appear to realise the object set before them- 
selves by the Committee—viz., to assist the extension of the use of the 
British Association system of screw-threads by making generally available 
accurate means for their verification. 
While recognising the excellence of the form of the British Associa- 
tion screw-thread for mechanical purposes, the Committee feel strongly 
that the difficulty of producing the form to the degree of accuracy desirable 
for the best class of work, and especially for gauge pieces, is a serious 
drawback to its value. Colonel Watkin’s photographs show very clearly that 
the best appliances in the most experienced hands that the Committee 
could find have failed to produce even single specimens of first-rate accu- 
racy. The letters addressed to the Secretary of the Committee by Mr. 
George M. Bond, manager of the standards and gauge department of the 
Pratt and Whitney Company, as well as the high reputation of his firm, 
leave no room for doubt that very great care has been taken to secure 
accuracy in these specimens. A considerable number of gauges made by 
English firms of good standing have been examined by the Committee, 
and have in every case shown errors of the same character as, though 
usually to a much greater degree than, the specimens submitted by the 
American firm. 
From several sources, and especially in Mr. Bond’s letters, it has been 
urged on the Committee that although the difficulties of constructing 
these gauges of a very high degrce of accuracy are practically insuperable, 
screw-threads of a flat-ended form can be produced with great exactness. 
A photograph taken by Colonel Watkin of a fine screw taken from an 
instrument made by Messrs. Brown and Sharpe shows that this is certainly 
the case. 
1899. HH 
