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.