The RAM Round Plate with Ball is constructed of powder-coated, marine-grade aluminum for durability and reliability in the most demanding environments. Each RAM round plate consists of a rubber ball connected to a round plate for marine use. FeaturesSize B, C: 2.5" round plate connects to RAM device holders containing the universal AMPS hole patternSize D: 3.68" round plate for drill-down mountingPowder-coated, marine-grade aluminum Backed by a lifetime warranty with RAM See size chart below for configurations