Keep commercial doors closing safely with this 3.5 in. x 3.5 in. Satin Nickel Steel Spring Hinge. A standard-duty steel, commercial grade door hinge, it's designed for automatic doors to securely self-close. This hinge is also UL R19063 listed for A label fire doors. The hinge functions as a full mortise single acting spring hinge and has a 5/8 in. radius.