The RAM-B-342-366U consists of a fork stem base, double socket arm and 1" diameter rubber ball, connected to a round plate with 1/4"-20 camera thread. The RAM® Motorcycle Fork Stem Base is one of the cleanest and most popular solutions for mounting your device cleanly on the center of your bike. This part is designed to fit into the cylindrical bore wall of fork stems and will work with stems that measure from 12 - 38mm (.5” – 1.49”).