Commercial door hinges steel spring square corner 4-1/2 x 4-1/2 inch. Ideal for use in corridors, entrances and stairways. Automatically closes door, an alternative to overhead mounted door closers. Patented ratchet adjustment eliminates need for adjustment locking pin. Meets NFPA8 standard for 3 hour fire rated doors -minimum 2 spring hinges per door required. UL listed for doors up to 4 feet x 8 feet weighing up to 180 lbs. Conforms to ANSI/BHMA standard A156.17, Grade 1.