The RAM-103U-D consists of the 1.5" C size diameter ball and socket system with one open socket end; RAM-201U-D socket arm is long length at 9.125" end to end with a 8" socket-to-socket length. This mount is designed to be used with any of the C size RAM Mount bases or cradles with a 1.5" diameter rubber ball. The RAM-202U RAM Round Plate Ball Base features industry standard AMPS hole pattern with 2.5" diameter base and can be used as an adapter to attach a holder, or a mounting drill-down base.