3/4x3/8 blk bushing. Malleable black iron pipe fittings. Larger size listing is for Male thread. Small size listing for Female thread. Ferrous Plugs, Bushings, and Locknuts, Fed. Spec. WW-P-471-B, ANSI B-16.14 (Dimensions), ANSI B-2.1 (Pipe Threads). 3/4" x 3/8"