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.