EMPLOYEE WAS TAKING JAM NUT LOOSE ON BOLT THAT HOLDS JAM BREAKER TO STRUCTURE WITH A 1"" DRIVE AIR WRENCH. THE JAM NUT CAME LOOSE CAUSING THE NUT TO TRAVEL UP THE BOLT. HIS RIGHT THUMB WAS PINNED BETWEEN PART OF THE TELEDYNE AND THE AIR WRENCH. HE HAD TO REVERSE WRENCH TO GET HIS FINGER BACK OUT