MBT-1 CS/SS Solid Machined Ball Transfer Unit 1" Main Ball Proudly made in the USA MBT-1 CS/SS Solid Machined Ball Transfer Unit, Main Ball is 1" Inch, 1" Main ball rotates on 1/8" support balls, MBT-1 CS/SS is integral flange at top allows unit to be dropped into a 1-3/8" diameter hole.