Hi Clarence The big ring gear was chrome plated steel, and the small gears were brass. I had a gear place in Milwaukee cut me a big ring gear for my #16 - a 20" gear with 600 teeth. I had them do it in stainless, and it has worked fine. Ron knows the machining and materials choices better than me though. I shot some images of the fans and gears and will get them off my camera soon.