EMPLOYEE REPORTED HE WAS INSTALLING PLASTIC BACK ONTO #10 TRIPPER HOT RAIL. AS EMPLOYEE HAND BACK AWAY FROM THE INSULATING PLASTIC, IT CAME INTO CONTACT WITH THE EDGE OF THE EXPANDED METAL GUA RD, CUTTING HIS LEFT INDEX FINGER KNUCKLE. INJURY BECAME RESTRICTED DUTY/ REPORTABLE ON 2-13-03 WHEN DOCTOR GAVE RESTRICTIONS OF ""NO GRIP WITH LEFT HAND"".