THE OPERATOR WAS ATTEMPTING TO REPLACE AUGER ON A GRIT SCREW USING A PIPE WRENCH WITH AN EXTENSION PLACED OVER THE PIPE WRENCH HANDLE FOR LEVERAGE. COWORKER WAS ASSISTING IN THE REMOVAL OF THE AUGER BY HAMMERING ON THE EXTENSION TO LOOSEN THE AUGER. THE OPERATOR'S HAND SLIPPED FROM THE PIPE WRENCH AND WAS CAUGHT BETWEEN THE PIPE WRENCH AND THE AUGER, TEARING HIS FINGERNAIL.