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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.
Each rack unit (U) is equivalent to 1 in (44 mm). Most rack rail is in sizes from 2 units high ( 3⁄43 in or 89 mm) to 45 units high ( 1⁄278 in or 2,000 mm). 3⁄4
Types of rack rail
In the USA, the commonly used form of rack rail is called Imperial rack rail. Imperial rack rail has round holes tapped for 10/32 UNF screws. In Europe, the common form of rack rail is full-hole rack strip which has square holes for M6 captive nuts.
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.