SBT-1 CS/SS 1/4" Stud Mounted Ball Transfer Unit 1" Main Ball 1/4"-20 Threaded Stem Proudly made in the USA SBT-1 CS/SS 1/4" Stud Mounted Ball Transfer Unit, Main Ball is 1" Inch, 1" Main ball rotates on (80) 1/8" support balls, SBT-1 CS/SS 1/4" stud mounted ball transfers is heavy duty, stud mounted bearing and capable of supporting as many as 75 pounds (per unit).