3 Legged Thing – Window Mount Clamp Kit w/AirHead Trinity, Darkness/Matte Black

Due to its spring loaded clamping, this cold shoe clamp enables one to one-handedly mount shoe fitted equipment very easily. Its finger screw serves both as a push knob for opening the clamp and for tightening down the clamping securely.
It fits the standard shoe sizes of 18, 20 and 22mm.
The Cold Shoe Clamp is tapped with 1/4″-20 and 3/8″-16 holes on the back side

Ercole M11-050A Umbrella Swivel Adapter with brass stud.

Ultralight AC-CSB ball clamp with black knob for large buoyancy arms