The Rack Unit is the way in which the Structured Cabling Rack is subdivided, allowing us to properly size the capacities of the components to be installed. One Rack Unit is equivalent to 1.75 inches. It is known by different names: U, UR, RU, UH, HU.
In the market we can find Structured Cabling Racks with capacities of 42U, 45U, etc.