The RAM zinc coated u-bolt rail base consists of the 1″ diameter ball and socket system with RAM Universal 1/4″-20 thread centered on a 2.5″ diameter plate. This mount is designed to be a universal mounting solution for both still and moving cameras. The base has a 1.0″ diameter rubber ball designed to sit at right angles to the mounting rail. The zinc coated metal u-bolt and nuts included will fit a circular rail with diameter from 0.5″ to 1.25″. To mount the rail base, place the top of the base on the rail and then slide the u-bolt around the rail, into the holes in the base top. Now tighten the screws onto the u-bolt until the base is clamped firmly. If you desire, you can now slot the black composite covers over the exposed ends of the u-bolt.Material: Powder Coated Marine Grade Aluminum Ball Size: 1″ Rubber Ball „B” Size Note: The „U” in the part number reflects product packaged in poly bag. The male 1/4″ long, 1/4″-20 thread in the middle of the 2.5″ diameter plate will connect to the standard female thread found at the bottom of most still and video cameras. Related Links: RAM Motorcycle Mounts PageRAM Camera Mounts Page RAM® double socket arms with their distinctive hour-glass shape are designed and recognized to provide the best possible performance for most any application.