Brown and Sharpe gauge

American wire gauge, American standard wire gauge, Brown and Sharpe gauge

A system used in the US for designating wire diameter in electrical wiring or the thickness of aluminum, brass, and copper sheets; ranges from 6/0 (0.58 in. or 16.3 mm) to 40 (0.0031 in. or 0.079 mm).
McGraw-Hill Dictionary of Architecture and Construction. Copyright © 2003 by McGraw-Hill Companies, Inc.