19-inch rack
The standard for open frame or enclosed cabinets used for the mounting of electronic equipment. Equipment must have a front panel that is 19 inches wide, including edges or ears that protrude on each side which allow the equipment piece to be mounted to the rack frame with screws. 19-inch racks in 2 post or 4 post form hold most equipment in modern data centers, ISP facilities and corporate server rooms.
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.
Front Mount vs Four Post
A front mount rack is a two post rack where equipment is mounted by the front plate of the equipment only, thus leaving the rest of the unit to hang behind the front plate. A key structural weakness of front-mounted support is the shear stress placed on the mounting rails and the leading edge of the equipment. As a result, 4-post racks have become common, with such racks featuring a mirrored pair of rear mounting posts.
Servers and deep pieces of equipment are often mounted using rails that are bolted to the front and rear posts. There is no standard for the depth of equipment, nor specifying the outer width and depth of the rack enclosure itself.
Dimensions
The standard electronic unit for mounting is 19" wide on the front plate. Behind the plate the remainder of the unit has to be less wide as to slide in between the posts. This width tends to be 16½ wide.
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.
- 16½" Equipment case chassis width
- 19" Equipment front plate width
- 18¼" Approx Horiz distance between equipment mounting holes
- 1¾" Equipment height per U, average between 1 and 5 U.
