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