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The height of equipment is described as being measured in the U, for one rack unit, which is 1.75 inches.Examples of rack mount equipment include, computer servers, internet routers, network hubs and switches, audio equipment such as a stereo amplifier, some tel-co equipment. The telecom industry tends to use a different rack width standard.The rack's two vertical parallel metal strips known as posts are each 0.625 inches wide, separated by a gap of 17.75 inches, giving an overall rack width of 19 inches. The posts have holes in them at regular intervals at a distance of 18.312 inches each. The holes in the posts are arranged vertically in repeating sets of three, with center-to-center separations of 0.5 inches, 0.625 inches, and 0.625 inches, a pattern repeating every 1.75 inches.Holes so arranged can either be tapped (usually 10-32 UNF thread, or, less often, 6mm metric) or have square holes for cage nuts.The height of equipment is described as being measured in the U, for one rack unit, which is 1.75 inches.* 18¼" Approx Horiz distance between equipment mounting holes* 1¾" Equipment height per U, average between 1 and 5 U.