THE EMPLOYEE WAS USING A BOLTER WRENCH TO BEND A ROOF BOLT THAT WAS HANGING FROM THE TOP. WHILE PUTTING UP PRESSURE ON THE BOLTER BOOM, THE WRENCH SLIPPED OFF THE BOLT AND BOOM WENT AGAINST THE TOP. HIS LEFT HAND WAS RESTING ON THE BOOM AND HIS MIDDLE FINGER GOT PINCHED AGAINST THE TOP.