Odd clamp given to me, need to know kind and use plz help!

The clamp opening is only two inches, the foot is brass on a ball and socket screw with a knob instead of a tommy bar or wing nut handle.... As for the anvil well the 4 pronged piece attached appears to be removable however, the clamp was given to me as is. The clamp itself seems to be made of aluminum. There are absolutely no markings anywhere! I'd love to know what it's used for please help ????