SIST EN 4590:2006

Overview

EN 4590:2005 is a European aerospace standard that specifies the characteristics of sheet metal spring retainers made from corrosion resisting steel, passivated, intended for use with self-locking barrel nuts (EN 4591). Prepared under AECMA (now ASD) and adopted by CEN, the standard defines configuration, dimensions, materials, surface treatment, marking and technical requirements for retainers used in aerospace fastener assemblies.

Key topics and requirements

• Scope and purpose: Retainers are spring, sheet-metal components that secure self-locking barrel nuts in aerospace structures; the standard covers their physical and material characteristics.
• Dimensions and configuration: Defines dimension series and masses (diameter codes such as 060 → 240) with corresponding geometric limits; dimensions are specified in millimetres and apply after surface treatment (see ISO 12280).
• Tolerances: Form and positional tolerances are specified in accordance with ISO 8788.
• Materials: Acceptable base materials reference EN 2540 (steel FE‑PM3902 X7CrNiAl17‑7) or EN 3638 (heat resisting alloy FE‑PA2601) as applicable.
• Surface treatment: Passivation and decontamination requirements follow EN 2516; retainers must be supplied in the passivated condition.
• Types and function: Two principal retainer variants:
  • Index type (Code A) - locates in the host hole to prevent rotation/vertical movement.
  • Clearance type (Code B) - used where nut access is available or where through-hole is undesirable; requires specified push‑out force when installed (values listed by diameter code).
• Marking and designation: Marking follows EN 2424 (style N). Example designation format: “RETAINER EN4590A060” (optional code I9005 may be inserted).
• Quality and approval: Manufacturer approval and product qualification reference aerospace quality standards EN 9100 and EN 9133.
• Normative references: ISO 5858, ISO 8788, ISO 12280, EN 2516, EN 2540, EN 3638, EN 4591, EN 2424, EN 9100, EN 9133.

Applications

• Aerospace OEM and Tier suppliers specifying or procuring spring retainers for barrel-nut fasteners.
• Mechanical designers and structural engineers who need compliant retention hardware for airframe, engine or service panels.
• Fastener manufacturers, quality assurance and procurement teams using the standard for acceptance criteria, marking and supplier qualification.
• Maintenance, repair and overhaul (MRO) organizations ensuring replacement retainers meet original specification.

Related standards

• EN 4591 - Self-locking barrel nuts (companion nut standard)
• EN 2516 - Passivation of corrosion resisting steels
• ISO 12280, ISO 5858, ISO 8788 - dimensional, procurement and tolerance references
• EN 9100 / EN 9133 - aerospace quality and qualification procedures

Keywords: EN 4590, aerospace retainers, spring sheet metal retainers, self-locking barrel nuts, corrosion resisting steel, passivated, fastener standards, EN 4591.