The RAP-B-121-224-1U consists of a yoke clamp base, 3.3" diameter suction cup base, standard length double socket arm and 2" x 1.7" square base that contains the universal AMPs hole pattern. The yoke clamp base will fit rails in diameter from 0.625" to a maximum of 1.25". The 1" rubber ball is at a right angle to the plane of the mount; when connected to a rail, the ball sits parallel to the rail. The suction cup is designed to have an extra strong hold on any smooth non-porous surface, but for best result, mount the suction cup on a glass or non-porous plastic surface.