EMPLOYEE STATED HE WAS USING THE HANDHELD HYDRAULIC WRENCH TO TIGHTEN A CABLE TRUSS BEING INSTALLED FOR ROOF SUPPORT WHEN HIS LEFT MIDDLE FINGER WAS CAUGHT BETWEEN THE TWIN PISTON RAM BLOCK AN D RAM CYLINDER HEAD STRAP PIECE DURING THE BACK STROKE/TENSION RELEASE OF THE CYLINDERS. THE INCIDENT RESULTED IN AN OPEN TYPE WOUND WITH NO FRACTURES.