HDBTSR-1 3/16 CS Ball Transfer Unit 1-3/16" Main Ball Exterior Sound Reduction Collar Proudly made in the USA HDBTSR-1 3/16 CS Ball Transfer Unit, Main Ball is 1-3/16" Inch, 1-3/16" Main ball rotates on 1/8" support balls, HDBTSR-1 3/16 CS is integral flange at top allows unit to be dropped into a1-3/4" diameter hole.