Racks - U Unit
The rack rails are divided vertically into 44.45 mm (1.75 in) high areas. Each area has 3 pairs of holes. The arrangement of the holes is shown in the drawing. Such area is commonly called U (unit), RU (rack Unit), in the German market HE (Höheneinheit). The height of the rack is determined by this unit. Hardware to be mounted in rack 19 or 10 inch rack is designed to occupy the total number of U units. For example, an oscilloscope or other diagnostic devices can be 4U high. Standard server cases range from 1 to 4U. Blade servers 10U. Patch panels 1U.
There are also 1.5U or 0.5U devices - eg patch panels. However, they are less common.
Rails or racks in the 10 or 19” rack standard are usually from 3 to 47U. The most common are hanging cabinets from 3 to 18U and standing cabinets 22/32/42U.
margin-top: 0px;" />
