The 72 fitting is suitable for most types of stair tread, including timber, open steel and checker plate. Fixing of the tread is by two bolt holes in each fitting. (Special order only.) Note: If Type 72 fittings are to be used for a permanent application or subjected to high loads, the stair tread support tube which is located at its ends with a single set screw, should be drilled and pinned to avoid rotational slip.