A Rack rail, or rack strip, is used to mount rackable electronic hardware and 19-inch rack mount accessories within a 19-inch rack. Within a rack a minimum of two rack rails are required to mount equipment. The height of rack rail is determined by the number of rack units required for mounting the equipment. The design of racks and rack rails is specified in ECIA - EIA/ECA-310 Each rack unit (U) is equivalent to . Most rack rail is in sizes from 2 units high () to 54 units high (). Types of rack rail Rack Rail comes in two different commonly used forms. 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. In both cases, rack screws and washers are required to mount rack mount equipment to the rack rail. 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. References https://standards.globalspec.com/std/902328/ecia-eia-eca-310 is a link to purchase the ECIA-ECA standard for racks and rack rails. http://www.kendallhoward.com/blog/The-Breakdown-on-EIA-310 provides background information on the standard. https://www.middleatlantic.com/search.aspx?q=rack%20rail&num=30&start=0&fc=RackUnits%3A54&cc=&ct= is a link to a source of 54 rack unit rails Computer enclosure Server hardware