The RAM Zinc coated U-Bolt Rail Base consists of the 1″ dia. ball and socket system with RAM Plastic Cradle for the Garmin GPS 45, 45XL, 48, 89, 90 and 92. The Rail 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 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.