NBT-1 1/2 CS Flange Mounted Ball Transfer Unit 1-1/2" Main Ball Proudly made in the USA NBT-1 1/2 CS Flange Mounted Ball Transfer Unit, Main Ball is 1" Inch, 1-1/2" Main ball rotates on (90) 3/16" support balls, NBT-1 1/2 CS is a heavy duty ball transfer unit, capable of supporting as many as 125 pounds (per unit).