Frequently Asked Questions

Rack Mounting Solutions

What is a Rack?

  • Open frame racks are structures onto which equipment is mounted using screws, cage nuts, or other mounting hardware.
  • Most rack-mounted electronic equipment have mounting widths of 19” (483 mm) or 23” (584 mm).
  • Common uses include server, telecom, broadcast video, lighting, audio, and scientific lab equipment. 
  • When equipment does not have the provision to be rack mounted, Hammond Mfg has many other options / accessories to help secure that equipment to the rack.  ie. shelves.

What is a Rack Unit (RU)?

  • A rack unit is the unit of measure that the rack industry uses to define vertical space. Often referred to as the number of “U” or “RU” to describe the mounting height of a rack or cabinet.
  • 1U = 1¾ inches (44.45 mm) in height. Example: A customer may ask for a 44U rack.
  • Rack units are often indicated as a number and/or as a marking.

Rack Units Height (in) Height (ft) Height (cm)
1U 1.75″ 0.15′ 4.4 cm
2U 3.5″ 0.29′ 8.9 cm
3U 5.25″ 0.44′ 13.3 cm
4U 7″ 0.58′ 17.8 cm
5U 8.75″ 0.73′ 22.2 cm
6U 10.5″ 0.88′ 26.7 cm
7U 12.25″ 1.02′ 31.1 cm
8U 14″ 1.17′ 35.6 cm
9U 15.75″ 1.31′ 40 cm
10U 17.5″ 1.46′ 44.5 cm
11U 19.25″ 1.6′ 48.9 cm
12U 21″ 1.75′ 53.3 cm
13U 22.75″ 1.9′ 57.8 cm
14U 24.5″ 2.04′ 62.2 cm
15U 26.25″ 2.19′ 66.7 cm
16U 28″ 2.33′ 71.1 cm
17U 29.75″ 2.48′ 75.6 cm
18U 31.5″ 2.63′ 80 cm
19U 33.25″ 2.77′ 84.5 cm
20U 35″ 2.92′ 88.9 cm
21U 36.75″ 3.06′ 93.3 cm
22U 38.5″ 3.21′ 97.8 cm
23U 40.25″ 3.35′ 102.2 cm
24U 42″ 3.5′ 106.7 cm
25U 43.75″ 3.65′ 111.1 cm
26U 45.5″ 3.79′ 115.6 cm
27U 47.25″ 3.94′ 120 cm
28U 49″ 4.08′ 124.5 cm
29U 50.75″ 4.23′ 128.9 cm
30U 52.5″ 4.38′ 133.4 cm
31U 54.25″ 4.52′ 137.8 cm
32U 56″ 4.67′ 142.2 cm
33U 57.75″ 4.81′ 146.7 cm
34U 59.5″ 4.96′ 151.1 cm
35U 61.25″ 5.1′ 155.6 cm
36U 63″ 5.25′ 160 cm
37U 64.75″ 5.4′ 164.5 cm
38U 66.5″ 5.54′ 168.9 cm
39U 68.25″ 5.69′ 173.4 cm
40U 70″ 5.83′ 177.8 cm
41U 71.75″ 5.98′ 182.2 cm
42U 73.5″ 6.13′ 186.7 cm
43U 75.25″ 6.27′ 191.1 cm
44U 77″ 6.42′ 195.6 cm
45U 78.75″ 6.56′ 200 cm
46U 80.5″ 6.71′ 204.5 cm
47U 82.25″ 6.85′ 208.9 cm
48U 84″ 7′ 213.4 cm

Mounting Types

  • Equipment can be mounted to racks and cabinets in various ways. There can be;
    • tapped rails,
    • round hole and
    • square hole rails.
  • It is important to confirm with your customer, what type of mounting rails they require.
  • Typically, open racks come with tapped  holes, whereas larger cabinets meant for heavy servers come with square holes for cage nuts.


Mounting Hardware

  • Rack screws are used to attach equipment directly to the tapped rack rails. There are several sizes of screws available, but 10-32, 12-24 and M6 are the most common. 
  • Square (cage nut) or round (clip nut) holes on rack rails, require the nut plus a screw in order to secure equipment to the rail.   
  • With square mounting holes, the screws connect to a removable cage nut placed in the required location on the rail.
  • With round holes, the screws thread into a removable clip nut that is placed in the required location on the rail.