The RAM Zinc Coated U-Bolt Rail Base consists of the 1″ dia. ball and socket system with RAM Plastic Cradle for the Compaq iPaq 2200 Series. The Aluminum Rail Base has a 1″ 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 1/2″ to 1.0″. For a larger rail, you can purchase the RAM-B-231LZS Large Rail Base for circular rails with diameter from 1/2″ to 1 3/8″.NOTE: This base is NOT rust proof. If you are looking to use this mount in the elements, we suggest the RAM-B-231 Stainless Steel U-Bolt Mount. Part number reflects product packaged in clear clam shell for store shelf display. For additional specifications, see components and drawings tabs.