General Tools GTM21 Sheet Metal Gauge Us Standard and Decimal Round 3 1/4"

The General Tools GTM21 is a sheet metal gauge, US Standard and decimal, round style, in hardened tempered steel, covering range 0 to 36, with a 3-1/4 inch diameter.

A sheet metal gauge is a slotted disc, and the slots are cut to the exact thicknesses of the standard gauge numbers. Slide the sheet into the slots until you find the one it fits, and read the gauge number off the disc.

The reason this tool exists is that gauge numbering is genuinely counterintuitive and cannot be reasoned out. Gauge numbers run backwards — a higher number is a thinner sheet — and the increments are not linear. Worse, the gauge scale differs by material: 16 gauge steel and 16 gauge aluminium are not the same thickness. This gauge is marked US Standard, which is the steel scale, and using it on non-ferrous material will give a wrong answer.

The decimal marking alongside the gauge number is what makes the tool practical, since drawings and specifications are increasingly written in decimals while stock and shop conversation remain in gauges. The disc translates between them.

Hardened tempered steel matters because the slots are the measurement. A gauge with worn or deformed slots reads wrong, and a soft one deforms.

Applications include sheet metal fabrication, HVAC ductwork, autobody, roofing, and general metalwork.

Users include sheet metal workers, HVAC technicians, fabricators, and autobody technicians.

Brand

General Tools

SKU

GTM21

Category

Hand Tools

Weight

0.3 lbs

Dimensions

6.50 x 1.50 x 0.50

Price

$29.00

Availability

In stock

Rating

4 / 5.0