The RAM® Add-A-Ball™ Accessory Ball for C Size Socket Arms (RAM-B-273-CU) allows you to connect another device to your existing C-size RAM® Mount. This ball is made up of a 1" ball connecting to a 5/16"-18 threaded stud that replaces the bolt in any Short or Medium C-size socket arm, and the ball connects to the middle of the socket arm on the opposite side of the tightening knob. If you are looking to mount more than one device but cannot locate multiple mounting points, this base is the ideal accessory for connecting both devices off of one mounting base.