EMPLOYEE WAS REMOVING A BROKEN 7/16""FASTENER FROM A STEERING FILTER HEAD ON A HAUL TRUCK. AN ADJUSTABLE WRENCH WAS BEING USED TO TURN THE EXTRACTOR. THE HARDENED MATERIAL BROKE IN A BRITTLE TYPE FRACTURE THAT PRODUCED A JAGGED EDGE THAT PROTRUDED FROM THE FASTENER ABOUT 3/8"". THE EE'S ARM CONTACTED THE JAGGED EDGE CAUSING A WOUND THAT REQUIRED 12 STITCHES.