Good morning, John;
I hope we are talking about the reducing bushing to go from a 3/8-16 threaded hole to a 1/4-20 hole to allow a European camera or a larger camera to be used with a tripod that has a 1/4-20 threaded post for holding the camera.
Two that I can suggest are the Gitzo G-1141 which I believe is made of steel, or the one by Wimberley that is made of brass. I do not recall the part number for the Wimberley. There are other companies who also make these adapters. Also ask at your local photo store. Ask them what theirs are made of.