BT-1 1/2 CS/SS Flange Mounted Ball Transfer Unit 1-1/2" Main Ball Proudly made in the USA BT-1 1/2 CS/SS Flange 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 1/2 CS/SS is flange-mounted ball transfer is a heavy duty ball transfer unit, capable of supporting as many as 250 pounds (per unit).