The EIA-310-D standard (often updated to EIA/ECA-310-E) defines the universal 19-inch rack specification, standardizing mounting dimensions, hole patterns, and vertical RU spacing for IT equipment compatibility. It establishes a 1.75-inch Rack Unit and a 17.72-inch minimum opening between rails, though it does not dictate overall cabinet depth or hole type. For a detailed breakdown of the standard, visit RackSolutions EIA-310: What Does It Mean? - Rack Solutions