A 1U device uses three vertically aligned mounting holes per side on the rack's square or tapped rails 3. While a rack unit is defined as inches (44. Thus, a 1U. You'll get the precise, standardized dimensions of a 1U server rack unit — including height (1. 26 cm), mounting hole spacing, and critical clearance allowances — plus actionable guidance on verifying physical fit, avoiding common installation errors, and selecting. Before installing system components, locate the hole pattern in the rack rails to allow adequate Unit height (U) of vertical space. AudioRax Rack Rail Pair, Cut-To-Order | 1/2U Spacing EIA-310 Standard The EIA-310 standard has served as the foundation for 19-inch equipment racks for over five decades.