The RAM-B-231ZU consists of a 1" rubber ball designed to sit at right angles to the mounting rail. The zinc coated metal u-bolt accommodates rails in diameter from 0.5" to 1.25" in diameter. Included are black cover caps to be placed over the exposed ends of the u-bolt and a composite adapter that can narrow the rail to a minimum width of 0.5". 

U-Bolt Dimensions:
Accommodates rails from 0.5" to 1.25" in diameter.