The several gauges are here given with explanation of their use.
The American Standard or Brown and Sharp's Gauge.—This gauge is commonly designated as A. W. G. or B. & S., and has been adopted by brass manufacturers and is used mostly in measuring brass, copper, silver, German silver, and gold in both wire and plate.
Birmingham or Stub's Wire Gauge (B. W. G.).—Old English Standard and Iron Wire Gauge. Birmingham or Stubs' Iron Wire Gauge is not the same as Stubs' Steel Wire Gauge. A table of Stub's Steel Wire Gauge is given on [page 741].
Fig. 823.—Micrometer screw gauge. It consists essentially of a screw whose thread is accurately turned to a pitch of some convenient fraction of an inch or centimetre. When the screw is screwed home, the surfaces of A and B meet, and the instrument should then read zero on both the straight and the circular scale. If this be not so, there is a zero error which must be either allowed for, or corrected by means of the screw provided for that purpose. If the former course be adopted, the reading of the instrument is taken when the faces A and B are in contact, and this number added to or subtracted from the final reading according to whether the error makes the wire apparently smaller or greater than its real size. The surfaces A and B are now screwed apart and then, after the wire to be measured (which should be clean and straight) has been introduced between them, they are screwed together to lightly grip the wire. If the gauge be screwed up too tightly the value of the measurement is destroyed, since a copper wire can easily be crushed, and in addition the accurate screw may be permanently damaged. To avoid the possibility of this happening, screw gauges are provided with a ratchet which prevents an excessive force being applied to the screw. If the pitch of the screw in the gauge be 1/20th of an inch, and the circular scale consist of 50 divisions, then for each revolution of the screw, the surface B will travel a distance equal to the pitch, that is 1/20th of an inch. The graduations on an instrument of this kind are generally 1/10th of an inch on the straight scale, with shorter lines to mark the half divisions. The thickness of a wire on the straight scale can therefore be read to the nearest 1/20th inch. Each division of the circular scale represents 1/50th of a revolution of the screw, which corresponds to a change in distance between A and B, of 1/50 of 1/20 = 1/1,000 in. If then the reading on the straight scale be 1 and on the circular scale 35, the distance between A and B is .1 + .035 = .135 inch.
Washburn and Moen's Standard Wire Gauge.—Commonly designated as W. & M. G. has been adopted by the U. S. Steel Corporation in making their wire.
New British Standard (N. B. S.).—British Imperial English Legal Standard and Standard Wire Gauge, and is variously abbreviated by S. W. G. and I. W. G.
Roebling Gauge.—Washburn Moen, American Steel & Wire Co.'s Iron Wire Gauge.
Figs. 824 and 825.—U. S. wireman's calculating gauge; views showing both sides. On the side shown in [fig. 824], set the required number of feet on the small circle opposite the required number of amperes on the large circle, then set the small pointer at the required voltage and loss. Then on the other side ([fig. 825]) the large pointer will indicate the required size of wire in B. & S. gauge, and will also indicate the safe carrying capacity, while the wire may be gauged by slot A ([fig. 824]).