Rack Rails

A EIA-compliant industry-standard rack enclosure will have two pairs of vertical mounting rails (one pair in front, one pair in back) that conform to the EIA standard for mounting hole spacing as shown below. The most important aspect of the diagram is the dimensions between mounting hole [center-to-center]. The diagram also shows the heights of a standard panel or piece of equipment, given as the U dimension [1U, 2U, 3U and 4U].

Rack Mounting Rail Hole Spacing
Rack Rail Hole Spacing

Standard Rack Height;; 21" to 84", in any 1 3/4" increments
Standard Rack (outside) Depth;; 17", 24", 29" and 36"
Standard Panel Widths: 482.6mm (19 inch), 609.6mm, 762.0mm (per EIA 310)
Standard Panel Widths: 19", 24", 30", adapters are available for mounting 23" equipment
Equipment Rack Manufacturers

Alternative Rack Mounting Rail Hole Spacing
Rack Hole Spacing Alternatives

There is another spacing, in addition to the Universal spacing, that may be found in an equipment rack, labeled as alternative spacing, as shown above. Note that there is still a common pair of holes at the same spacing, but the intervening hole is absent. The alternative spacing limits the placement of equipment or rack panels. In addition the spacing could result in a gap between blank panels or equipment placed one atop another.

EIA-310 does not specify rack depth. So be sure to specify or know the internal depth, usable depth and overall depth.
Height is also given in 'U', 1U = 44.45mm, 2U = 88.90mm

PC motherboard

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