Ram Mount 3.25-Inch Diameter Suction Cup Twist Lock Base (Black) Consists of a 3.25 inch twist lock suction cup base. Connect to the RAM-B-238U diamond base with a 1 inch rubber ball. The suction cup is designed to have an extra strong hold on any smooth, non-porous surface. For best results mount the suction cup on glass or non-porous plastic surface.