The Marine Grade Aluminum Rail Base has a 1.0'' diameter Rubber Ball designed to sit at right angles to the mounting rail, and comes with two separate u-bolts to accomodate any bar or railing up to 1" or 1.25" in diameter, respectively. Also included is the RAP319 plastic adapter, which will allow you to mount on a bar or railing with a diamter as small as 0.5".
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. Now tighten the screws onto the u-bolt until the base is clamped firmly. If you desire, you can slot the black plastic covers over the exposed ends of the u-bolt.
Dust or wipe clean with a cloth dampened with water once a week. Be sure not to leave water spots on the surface. These water spots will dry and could possibly leave permanent marks. Clean stains/spots using the following steps: Dampen a soft cloth with a mixture of hot water and liquid dishwashing detergent. Wring the cloth as much as possible to remove excess liquid. Rub the surface lightly in a circular motion. Dry the surface immediately with a clean, soft towel.