4U

4U brands include Buchla, CGS, CLee, EMS, Hexinverter Électronique, Kilpatrick Audio, Loudest Warning, Metasonix, MFOS, Polyfusion, Serge, Slightly Nasty and YuSynth.

Module dimensions
The height of 4U format synthesizer modules is four standard rack heights or 7 inches, (177.8 mm). Buchla modules are multiples of 4.25" wide, and most Serge modules are full-width panels that are 17" wide (they occupy the full space within a 19" rack's mounting hardware).