Nosings at treads, landings and flfloors of stairways shall have a radius of curvature at the nosing not greater than 9/16 inch (14 mm) PHOTO 21 or a bevel not greater than 1/2 inch (12.7 mm) PHOTO 22. A nosing projection not less than 3/4 inch (19 mm) and not more than 11/4 inches (32 mm) shall be provided on
stairways PHOTO 23. The greatest nosing projection shall not exceed the smallest nosing projection by more than 3/8 inch (9.5 mm) within a stairway PHOTO 24.
Exception: A nosing projection is not required where the tread depth is not less than 11 inches (279 mm).