RAM Mount GoPro Hero Short Arm Flat Surface Mount [RAM-B-138-A-GOP1U]RAM Flat Surface Mount, Short Double Socket Arm & 1" Diameter Ball with Custom GoPro Hero Adapter The RAM B 138 A GOP1U consists of a 2. 5" diameter round base with the universal AMPS hole pattern, SHORT size double socket arm and 1" diameter ball with custom GoPro Hero adapter. 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