Most rack rail is in sizes from 2 units high (3+1⁄2 in or 89 mm) to 54 units high (78+3⁄4 in or 2,000 mm).
Tapped/threaded rack rail has round holes tapped for 10-32 UNF or 10-24 UNC screws.
The other common form of rack rail is square hole rack strip which has square holes for captive nuts, available tapped for various different screw threads, that are clipped into the holes as needed to mount equipment.
The size and strength of rack rail is determined by its application.
Increased thickness of steel results in stronger rack rail and varieties of rack rail can be found such as double angle and single angle rack rail.