NMBT-5/8 CS Solid Machined Ball Transfer Unit 5/8" Main Ball Proudly made in the USA NMBT-5/8 CS Solid Machined Ball Transfer Unit, Main Ball is 5/8" Inch, 5/8" Main ball rotates on 3/32" support balls, NMBT-5/8 CS is integral flange at top allows unit to be dropped into a 1" diameter hole.