National Hardware N287-146 4 in. Pro Series Self Closing Hinge, Oil Rubbed Bronze Pro Series spring hinge manufactured with cold-rolled steel, Closing speed is adjustable Fits standard hinge cutout and holes, Tension is adjustable, 5/8 inch radius round corners Hinge is UL approved for fire doors which must use a minimum of 2 spring and one conventional hinge Doors weighing to 50 pounds require 1 spring hinge, to 85 pounds require 2 hinges, 110 pounds need 3 Additional hinges used must also be 4 inch. Designed for doors measuring up 3 feet by 7 feet