2.5" diameter round base with the universal AMPs hole pattern, double socket arm and connecting Humminbird/Apelco marine adapter base. The mount is designed with a RAM 1" diameter patented rubber ball and socket system that has adjustment points at both ends of the double socket arm; this allowing for almost infinite adjustment and perfect viewing angles. The RAM-B-107 is a "LIGHT USE" mount, designed to hold smaller marine electronic devices. This mount is compatible with the following electronic devices: Humminbird 700 Series Humminbird 500 Series Humminbird 300 Series Humminbird 100 Series Humminbird Matrix Series (excluding Matrix 97) Lowrance Elite-5 Lowrance Elite-5M Lowrance Elite-5X Raymarine Apelco Fishfinder with matching hole pattern. Ball Size: 1" Rubber. "B" Ball Size. Material: Powder Coated Marine Grade Aluminum