Doors are Fire Rated by Underwriters Laboratories Inc., for 1-1/2 hours * Door and Frame are fabricated from 16 gage, galvannealed steel with a prime coat finish. * Wall Opening Minimum Requirement 14-3/8" x 14-3/8" * Concealed Hinge operates completely out of sight so that only the door and frame is visible. * Door has a heavy duty spring to assure positive latching.