1-1/2" Stud Type Ball Transfer Unit 3/8" Threaded StemNSBT 1 1 2 CS Stud Mounted Ball Transfer Unit 1 1 2" Main Ball 3 8" 16 Threaded stem Proudly made in the USA NSBT 1 1 2 CS Stud Mounted Ball Transfer Unit, Main Ball is 1 1 2" Inch, 1 1 2" Main ball rotates on (90) 3 16" support balls, BT 1 1 2CS stud mounted ball transfer is a heavy duty ball transfer unit, capable of supporting as many as 250 pounds (per unit). SBT 1 1 2CS features a 1 and 1 2 inch ball bearing resting on 90 individual support