AT APPROX 1:15 A.M. ON 6/28/00, EMPLOYEE WAS IN PACKHOUSE WORKING ON THE 2 YD. MIXER. HE & ANOTHER EMPLOYEE WERE ATTEMPTING TO REMOVE LID BOLTS; THE LAST ONE STUCK SO HE HELD A WRENCH ON IT & THE OTHER EMPLOYEE STRUCK WRENCH WITH A 4# HAMMER TO BREAK IT LOOSE. WRENCH SLIPPED & INJURED'S HAND WAS PINCHED BETWEEN THE WRENCH & A METAL STRAP ON THE LID, CAUSING CONTUSION.