BT-1 CS/SS Flange Mounted Ball Transfer Unit 1" Main Ball Proudly made in the USA BT-1 CS/SS Flange Mounted Ball Transfer Unit, Main Ball is 1" Inch, 1" Main ball rotates on (80) 1/8" support balls,BT-1 CS/SS is is a heavy duty ball transfer unit, capable of supporting as many as 75 pounds (per unit).