The holes on the mounting rails are not spaced evenly. Instead, they follow a repeating 3-hole pattern per Rack Unit: Top hole to middle hole: 0.625 inches (15.88 mm) Middle hole to bottom hole: 0.625 inches (15.88 mm)
Following the dissolution of the EIA, the Electronic Components Association (ECA) maintained the standard. It is currently managed by the Electronic Components Industry Association (ECIA) and is frequently adapted into global standards like IEC 60297 and DIN 41494. Eia Eca-310-e Pdf
Square-hole cabinets (which are now industry standard over threaded holes). Improved cable management space. More accurate tolerances for mounting equipment. Where to Find the EIA/ECA-310-E PDF The holes on the mounting rails are not spaced evenly
The main purpose of the document is to standardize dimensions so that equipment from any manufacturer will seamlessly mount into a rack built by any other manufacturer. Core Technical Specifications of EIA-310-E Square-hole cabinets (which are now industry standard over
The primary goal of EIA-310-E is to ensure interoperability between equipment from different manufacturers. It standardizes several critical dimensions for 19-inch racks: