THREE EE'S WERE PULLING A 3' X 7"" METAL PLATE WITH A COME-ALONG FOR OUTSIDE FOR #4 BIN. A 2"" X 12"" BOARD WAS BEING USED AS A GUIDE FOR THE PLATE TO SLIDE ON. ONE EE PULLED THE COME-ALONG & THE OTHER TWO EE'S GUIDED THE PLATE ACROSS THE HAND RAIL. THE PLATE SLIPPED AND ONE EE GOT L THUMB CAUGHT BETWEEN THE BOARD & METAL PLATE. RESULTED IN LACERATION REQUIRING SUTURES & MODIFIED DUTY