Steel: Manufacturers' Standard Gauge for uncoated carbon steel sheet (hot/cold rolled).
Galvanized: Manufacturers' Standard Gauge for galvanized sheet; values include the zinc coating.
Stainless: U.S. Standard Gauge. Many suppliers instead sell stainless to the steel MSG values
(e.g. 16 ga = 0.060" vs. 0.0625") — confirm with your supplier when it matters.
Aluminum: Brown & Sharpe (same as AWG). Aluminum is usually ordered by decimal thickness
(0.032, 0.040, 0.050, 0.063, 0.080, 0.090, 0.125…), so specify thickness, not gauge.
All values are nominal; mill tolerances apply. Gauge numbers are not comparable across materials.