Malleable iron. Regular plugs hollow core design. Meets standard specifications. Fed. Spec. WW-P-471-B, ANSI B-16.14 (Dimensions), ANSI B-2.1 (Pipe Threads), Ferrous Plugs, Bushings, and Locknuts, Fed. Spec. WW-P-471-B, ANSI B-16.14 (Dimensions), ANSI B-2.1 (Pipe Threads), Malleable Iron Unions (Class 150), Fed. Spec. WW-U-531C, ANSI B-16.39.
