A quick disconnect clamping assembly for releaseably attaching an accessory to an elongate support such as a picatinny-style mounting rail comprising a clamp body with a mounting yoke that is adapted to slide over and receive the picatinny rail. The yoke includes a substantially rectangular base plate defining the central upper surface of the clamp body and includes a pair of parallel sidewalls extending upwardly therefrom. A pair of spaced slots formed in the inner surfaces of the sidewalls are adapted to receive a spring and a spring biased positioning ball acts to precisely position the clamping assembly on the mounting rail.