INJURED EE AND ANOTHER EE WERE TIGHTENING WEDGE BOLTS AT PRIMARY JAW CRUSHER WITH A 3/4 DRIVE RACHET AND SOCKET. THE SOCKET SLIPPED OFF THE NUT AND INJURED EE'S LT. INDEX FINGER; WAS MASHE D BETWEEN THE CHEATER PIPE THAT WAS ON THE RACHET AND THE BEARING HOUSING OF THE JAW.