2.5" Composite Round Base w/AMPS Hole Pattern & 1.5" Ball The RAP-202U consists of a 1.5" diameter rubber ball connected to a flat 2.5" diameter base. This mount has pre-drilled holes, including the universal AMPS hole pattern. Material: High Strength Composite Ball Size: 1.5" Rubber Ball Size Note: The "U" in the part number reflects product packaged in poly bag.