NCBT-1 1/2" SS Flange Mounted Ball Transfer Unit 1 1/2" Main Ball Proudly made in the USA NCBT-1 1/2" 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, NCBT-1 1/2" SS is a heavy duty ball transfer unit, capable of supporting as many as 125 pounds (per unit).