The RAM-201U-B consists of a Short length double socket arm that accommodates 1.5" C size ball bases, device holders, and adapters. A single spring inside the arm keeps the socket open, and allows you to insert the ball into the socket connection. This arm has an overall length of 5.69". The easy to adjust knob allows for near-infinite adjustability.This RAM-246U consists of a 1.5" rubber ball, connected to a 4.75" square plate with 4x100mm holes and 4x75mm holes in each corner