EMPLOYEE WAS STANDING ON TOP OF THE RIGHT HAND ROLLER FRAME OF CAT D-11 DOZER. HE WAS DRIVING A PIN INTO THE HARD BAR TO SWING THE FRAME. AS HE HIT THE PIN, A SMALL PIECE OF METAL CAME OFF OF THE PIN AND STRUCK HIM IN THE CALF OF HIS RIGHT LEG. THE METAL HAD TO BE REMOVED BY A PHYSICIAN.