General Tools 21 US Standard Sheet Metal Round Gage This sheet metal gage is designed to accurately determine the thickness of uncoated sheet metal, plate iron and steel Gage numbers are US Standard 0 to 36, based on weights in ounces per square inch Decimal equivalents of each size are stamped on the reverse side of the sheet metal gage This standard sheet metal gage is 3-1/4" in diameter and 3/32" thick Featuring a satin finished, this sheet metal gage is made from hardened and tempered heavy gage steel