EE WAS INSTALLING A BUCKET TOOTH. HE WAS USING AB&O HAMMER TO DRIVE THE TOOTH RETAINER PIN INTO PLACE. HE WAS HOLDING THE RETAINER PIN IN PLACE WITH HIS RT. HAND AND AS HE STRUCK THE PIN WITH THE HAMMER, THE HAMMER SLIPPED OFF THE PIN AND STRUCK HIS THUMB. HE WAS TRANSPORTED TO OCCUPATIONAL MEDICINE & X-RAYS REVEALED A ""TUFT FRACTURE"" ON HIS THUMB. PLACED ON RESTRICTED DUTY.