7.4.7 Openings.
Openings in trail tread surfaces, trail resting spaces, and trail passing spaces shall be small enough to prevent passage of a 1/2 inch- (13 mm-) diameter sphere. Where possible, elongated openings should be placed perpendicular, or as close to perpendicular as possible, to the dominant direction of travel.
Exception: Where openings that do not permit the passage of a ½ inch (6.4 mm) sphere cannot be provided due to a condition for an exception, openings that do not permit passage of a ¾ inch (19 mm) sphere shall be permitted.
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