Connect another device to your existing RAM® Mount with the RAM-B-273U Ball Base Adapter. This ball is made up of a 1" ball connecting to a 1/4"-20 threaded stud with a length of 1.6". The threads on this ball replace the bolt in any B-size socket arm, and the ball connects to the middle of the socket arm on the opposite side of the tightening knob.
eBay