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Network Rack Hole Spacing

Fiber optic splice closure knowledge brief Published 03 Aug 2020

Prepared for preliminary research by the RIVO OPTICAL knowledge desk. Confirm cable count, splice capacity, sealing class, tray layout, protection sleeves and installation requirements against current standards and product documentation.

Standard 19-inch network racks follow the EIA-310 specification, with vertical hole spacing in repeating patterns of 0.5", 0.625", 0.625" per rack unit and horizontal spacing of 18.312" center-to-center.Rack Unit and Vertical Hole Spacing
  • Rack Unit (U): 1U = 1.75 inches (44.45 mm) in height .
  • Vertical Hole Pattern: Each 1U contains three holes with center-to-center spacing of 0.5" (12.7 mm) and 0.625" (15.9 mm) alternately, forming a repeating pattern: 0.625" – 0.625" – 0.5" .
  • Half-Unit Spacing: Some racks use 1/2U spacing (0.875") for improved ventilation and flexibility .
  • Measurement Reference: The start and end of a 1U space is measured from the center of the first 0.5" hole .
Horizontal Hole Spacing
  • Distance Between Vertical Rails: 18.312 inches (465.1 mm) center-to-center .
  • Rack Opening Width: Minimum 17.72 inches (450 mm) inside the rails .
  • Front Panel Width: Standardized at 19 inches (482.6 mm) for all rack-mounted equipment .
Hole Types
  • Square Holes: Most common; compatible with cage nuts or clip nuts .
  • Round Holes: Require clip nuts; less common .
  • Threaded Holes: Some racks have pre-tapped holes, but spacing follows the same EIA-310 pattern .
Summary Table of Standard Rack Hole SpacingParameterMeasurementRack Unit (1U) Height1.75 in (44.45 mm)Vertical Hole Pattern0.625" – 0.625" – 0.5" (center-to-center)Horizontal Rail Spacing18.312 in (465.1 mm) center-to-centerRack Opening Width≥ 17.72 in (450 mm)Front Panel Width19 in (482.6 mm)Hole TypesSquare, Round, or ThreadedNotes
  • The vertical hole pattern repeats for each U, ensuring consistent mounting for devices of varying heights.
  • Rack depth varies by manufacturer but typically ranges from 26" to 32" to accommodate rear-mounted equipment and airflow .
  • Proper understanding of these measurements ensures interoperability between different manufacturers' equipment and racks. This table and specifications provide a complete reference for designing, installing, or verifying network and server rack compatibility.

Network Rack Hole Spacing - RIVO MULTITRADE OPTICAL SYSTEMS [PDF]

Network Rack Hole Spacing

Rack Specifications

To help with cable management, allow additional space in the rack above and below the chassis to make it easier to route all of the

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Technical note

This reference is intended for preliminary fiber optic splice closure research. Compatibility, splice capacity, sealing class, tray layout, protection sleeves, installation methods, test limits and applicable standards must be verified for the specific project.

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