5U

5U is the term used for modules or equipment that is five standard rack units high. 5U modules typically use 1/4" connectors and plugs for patching.

Dimensions
The common 5U modules are exactly 8.75" (222.25mm) high, although non-American manufacturers may prefer 220mm or 230mm. The format is called 5U because 8.75" is equal to five vertical units in a standard 19" equipment rack.

The width of a single width 5U modules varies. Some manufacturers use the width of the original Moog modules (1U = 2.125"), and as such, these fall into a sub-format called MU (for Moog Unit). MU module manufacturers include Synthesizers.com, Club Of The Knobs, Krisp1, Mos-lab, Moon Modular, STG Sound Lab, and ModuSonics. Other 5U manufacturers, like Synthesis Technology MOTM, Oakley Sound Systems and Modcan B-series, use a slightly narrower width of 1.75".

Power considerations
Most 5U modules use a +/- 15v power supply, some also need 5v.