4 Inch spring adjustable self closing door hinge, manufactured with cold rolled steel, closing speed is adjustable, fits standard cutouts, tension is adjustable, 1/4 inches radius round corners. Hinge is UL approved for fire doors which must use a minimum of 2 spring and one conventional hinge per door. Doors weighing up to 50 pounds require 1 spring hinge, doors up to 85 pounds require 2 spring hinges. Doors up to 110 pounds require 3 spring hinges. Conforms to ANSI/BHMA Standard A156.17-2004. *NFPA-80 requires fire labeled doors to have a minimum of 2 spring hinges. NOTE: All hinges must have pivot points aligned for smooth operation. Always use same hinge sizes.