A MAINT MECHANIC WAS ROLLING OPEN 30"" BLIND FLANGES. HIS TOOLS WERE A 2"" BOX END/ OPEN WRENCH. AS HE REMOVED THE LAST FLANGE BOLT, THE FLANGE ROLLED AND CAUGHT HIS RIGHT MIDDLE FINGER BETWEEN THE FLANGE AND THE WRENCH. EE JERKED HIS FINGER OUT OF THE PINCH POINT CAUSING A LACERATION THATREQUIRED SIX STITCHES. NO LOST TIME; RESTRICTED DUTY.