These butterfly (ball) clamps are made to clamp two 25mm (1 inch) ball mounts; which is a standard size for scuba diving camera accessories.  They allow mounting of camera trays to ball arms, or ball arms to torches, strobes, etc.  These clamps are made from aluminium and black anodised for corrosion resistance and have stainless steel springs. 

The two halves of the clamps are set at angles to each other which give a greater range of movement side to side (up to 60 degrees) when compared to a standard flat type of butterfly clamp.