MBT-5/8 CS Solid Machined Ball Transfer Unit 5/8" Main Ball Proudly made in the USA MBT-5/8 CS Solid Machined Ball Transfer Unit, Main Ball is 5/8" Inch, 5/8" Main ball rotates on 1/8" support balls, MBT-5/8 CS is integral flange at top allows unit to be dropped into 1" diameter hole.