530 REPORT—1896. 
showed also how the angle of the thread could be accurately verified by 
this method by having suitable hairs. 
2. The Works Manager. 
The Committee, after considering various methods, came to the con- 
clusion that male gauges for ordinary workshop use were best tested, as 
regards pitch and form of thread, by a template or ‘comb’ for each number, 
the accuracy of which has been verified by the photographic method. 
The screw to be tested is placed against the teeth of the comb, and the 
correctness of its fit verified by the eye against a light background. 
The external dimensions of the screw can be obtained by any good 
micrometer gauge, and the internal diameter or core by a gauge such as 
that which is described in the Appendix by Mr. Stroh. 
The Committee have failed to discover any very reliable method of 
testing, to any degree of accuracy, a female standard gauge. No clearance 
was allowed in the original definition of the system between the male 
and female standards. Hence a mathematically accurate male gauge 
cannot be screwed into a mathematically accurate female gauge. But 
by allowing a certain margin—a maximum and minimum diameter—an 
internal compatibility of dimensions is allowed in the workshop gauges, 
which is of a sound, practical character. The female screw must always 
be a little larger than the standard male gauge, but this must never exceed 
what is known as a ‘ good fit.’ 
A working margin is given in Appendix III. by a table prepared by 
Mr. Le Neve Foster. 
Mr. Price, on behalf of the Committee, has made a series of measure- 
ments of certain sizes of B.A. screws which show the limits within which 
they are obtained in practice. His measurements indicate that the 
variation from the full diameter, which must be allowed for necessary 
inequalities in manufacture, is not a function of the diameter, but is rather 
in the nature of a constant quantity. This quantity appears to be 
approximately 1 mil. below the full diameter for all brass screws of sizes 
Nos. 0 to 11, and 1-5 mil. for all iron and steel screws of the same sizes. 
3. The Workman. 
The measuring gauge, available to the workman as well as to the fore- 
man, is one that need not possess the mathematical accuracy of the 
standard gauges, but nevertheless it must not be allowed to deteriorate 
or to maintain false belief in its accuracy. Those that are subject to 
pressure and friction must necessarily wear, become distorted, and, in 
time, inaccurate. Hence the Committee were anxious to obtain a mode 
of comparison which would be free from this source of error. The most 
important measurement, whose accuracy should be easily verified by the 
workman is that of the pitch, and this is easily effected with the ‘half- 
nut gauge’ described in Appendix II. 
The Committee are pleased to find that the result of their inquiry and 
discussion enables them to recommend for general use means of comparison 
which do not involve the wear and deterioration of the gauges. Defor- 
mation is confined to the taps and screw-plates, and as frequent verifica- 
tion of the manufactured screw is desirable continued accuracy is insured. 
With the introduction of simple methods of comparison and measurement 
errors in the screws issued and want of interchangeability are rendered 
improbable in a well-regulated shop, and unnecessary in any place. 
There remains now to determine a place where material standard 
