GY3 and others. Here's the disc hub cap that I had spun. It was a simple flat stock aluminum cut out to a round disc with enough radius to be put on a lathe and spun into shape. I forgot the type of machine that shapes it though. When I got it, the 4-1/2 inch bolt pattern was not in it. I placed them in the flat part of the Auto drag centerline wheel and centered the main axle hole and lug bolt holes. I then had to drill 'em out.
I can post pictures of study drawings on how this was proposed to the machinist.