1" galv locknut. Malleable iron. Standard Malleable Iron Fittings, Fed. Spec. WW-P-521F, ANSI B-16.3 (Dimensions), ANSI B-2.1 (Pipe Threads), ASTM A-197 (Chemical & Physical Properties), ASTM A-153 (Galvanizing), Ferrous Plugs, Bushings, and Locknuts, Fed. Spec. WW-P-471-B, ANSI B-16.4 (Dimensions), ANSI B-2.1 (Pipe Threads). 1"