420UNP Finish: Unplated Features: -Matl. Thickness of 2", 90/180 min UL Fire Rating, 1 each.-Additionally, they can be used on wood core doors.-Specifically designed with square edges for metal doors.-Use at least one fire-rated hinge for every 20" of door height.-Used on hollow metal, sheet metal, tin clad and steel composite swinging type fire doors.-Not to be used on a door that normally is held open.-One hinge for every 60 lbs.-Whichever calculation demands more hinges.-Frames rated up to and including 3 hours.