EN 3633:2008

Overview

EN 3633:2008 - Aerospace series: Installation hole for fluid fittings, flanged - is a European (CEN) standard that defines the geometric and drawing requirements for installation holes, bosses and installation recesses used with flanged fluid fittings specified in EN 3630 and EN 3631. The document covers hole dimensions, tolerances, recommended edge treatments and the prescribed method for callout and designation on engineering drawings.

Key topics and technical requirements

• Scope: Specifies dimensions and design features for installation holes and surrounding bosses/recesses intended for flanged fluid fittings (straight and 90° elbow types referenced via EN 3630/EN 3631).
• Hole dimensions and tolerances: Detailed hole geometry and dimensional codes are provided (see Table 1 in the standard). Tolerancing guidance uses classes such as H11 and instructions like “use N < E only if strictly necessary.”
• Edge treatment: Sharp edges are to be broken to specified radii (0.1 mm to 0.3 mm) to avoid stress concentrations and sealing issues.
• Boss and recess design: Profiles, depths and clearance features for bosses and installation recesses are defined to ensure correct seating and sealing of flanged fittings (figures illustrate typical boss and recess cross-sections).
• Drawing callout and designation: Section 6 prescribes example callouts and a standard designation format (e.g., EN 3633 - 140 - 3) for inclusion in description and identity blocks on engineering drawings.
• Normative references: Directly linked to EN 3630 and EN 3631 as indispensable for correct application.

Applications and users

• Who uses EN 3633:2008

  • Aerospace structural and systems designers specifying fluid system interfaces.
  • Mechanical and manufacturing engineers responsible for panel and component fabrication.
  • Detail drafters and CAD modelers preparing installation drawings and callouts.
  • Quality assurance, inspection and certification teams verifying compliance.
  • Procurement and suppliers of flanged fluid fittings and machined components.

• Practical applications

  • Defining installation hole layouts and boss/recess geometry in airframe panels and equipment mounts.
  • Ensuring consistent sealing and mechanical support for flanged fluid fittings in fuel, hydraulic and pneumatic lines.
  • Standardizing drawing annotations and part designation to streamline manufacturing and inspection.

Related standards

• EN 3630 - Fluid fittings, flanged, straight - O‑ring sealing for 0.8 mm thick tubes
• EN 3631 - Fluid fittings, flanged, 90° elbowed - O‑ring sealing for 0.8 mm thick tubes

Using EN 3633:2008 helps aerospace teams achieve repeatable, compatible interfaces for flanged fluid fittings and ensures clear, standardized communication on engineering drawings.