Yoke Clamp Base with 1 inch Rubber Ball and 1/4-20 inch Tapped Socket to add another Ball The RAM-B-121BA, yoke clamp mount with an added 1/4 inch -20 thread to add another ball base (RAM-B-237). This clamp will fit rails from 0.625 inch to 1.25 inch in diameter. The 1 inch rubber ball is set at a right angle to the plane of the mount, so when connected to a rail, the ball sits parallel to the rail. Material. Marine Grade Aluminium. Ball Size. 1 inch
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