one inch stainless steel main ball rotates on a bed of 1/8 inch stainless steel support balls in a stainless steel machined cup. The cup and cover are hardened. Hudson bearings is an innovative domestic manufacturer of ball transfers. the mbt ball transfer features a machined housing that is hardened and plated with a stamped metal cap. integral flange allows unit to be dropped into a 1.410 inch hole. housing option includes stainless steel. ball options include stainless, nylon, phenolic, and delrin.