EIA-310-D was officially withdrawn in 2012, but its dimensions are still widely used. For free reference :
For most IT deployment and rack-buying decisions, purchasing the raw document is unnecessary. The critical tolerances, dimensions, and spacing values detailed in this article provide the functional data needed to ensure hardware compatibility. eia310d standard pdf
The mounting holes on a rack’s vertical rails are not spaced evenly. Instead, they follow a repeating 1U pattern. Within every 1.75-inch Rack Unit, there are three holes spaced as follows: 0.625 inches (15.875 mm) Middle to bottom hole: 0.625 inches (15.875 mm) Bottom to top hole of the next U: 0.500 inches (12.700 mm) EIA-310-D was officially withdrawn in 2012, but its
Vertical space in a server rack is measured in Rack Units, abbreviated as "U" or "RU." The mounting holes on a rack’s vertical rails
When manufacturing custom server rack accessories or validating third-party infrastructure, use this checklist to ensure complete EIA-310-D compliance. Imperial Metric Metric Equivalent Notes / Constraints Tolerance: ± 0.03" Hole Center-to-Center Must be precise for bolt alignment Chassis Clearance Width ≤is less than or equal to ≤is less than or equal to Equipment body must stay under this width Total 1U Height Accumulates perfectly over 42U or 48U Outer Hole Spacing Space from Hole 1 to 2, and Hole 2 to 3 Inner Hole Spacing Space bridging the boundary between separate units 5. Summary and How to Source the Document
The EIA-310-D standard establishes a repeating vertical hole pattern for every 1U of space. Each Rack Unit contains three distinct screw holes. The spacing between these three holes is not uniform, which is a common point of confusion for beginners: 0.625 inches (15.88 mm) Hole 2 to Hole 3: 0.625 inches (15.88 mm) Hole 3 to Next U Hole 1: 0.500 inches (12.70 mm) This creates a total repeating pattern height of 4. Hole Shapes and Sizes
Commonly found in telecommunication racks and AV environments, these rails feature pre-tapped round holes. The most common thread sizes are #10-32, #12-24, or metric M6.