ISO 9634:1994

Overview

ISO 9634:1994 - "Aerospace - Fluid systems - Dimensions of plastic protective caps and plugs" specifies the configuration and dimensional requirements for plastic caps and plugs used to protect openings in aerospace fluid-system components during transit and storage. The standard covers both threaded and non‑threaded protective devices for smooth or threaded openings, tube ends and hose fittings, and includes figures and tabulated dimensions for common MJ thread sizes.

Key topics and requirements

• Scope: Protection of fluid-system components (orifices, equipment ports, tube ends, rigid and flexible piping) to preserve threads and sealing surfaces and prevent ingress of foreign matter during handling, transport and storage.
• Device types: Defines bouchons (threaded plugs) and capuchons (non‑threaded caps) for internal and external protection.
• Threaded protections: Dimensions and configurations for interior and exterior threaded caps intended for cone fittings and MJ series threads (document tables cover MJ8 up to MJ50).
• Smooth openings and tube ends: Standardized cap shapes and size codes for non‑threaded protection of smooth ports and tube ends.
• Design detail: Includes Figures 1–4 and Tables 1–4 with minimum/maximum values for dimensions such as A, B, C, D, F, L and profile/face contact geometry. Tolerances for thread combinations are referenced to applicable product standards.
• Manufacturing and fit: Dimensions selected to allow manual fitting and compatibility with manufacturing tolerances; elliptical forms allowed within specified limits for some sizes.
• Informative annex: Annex A provides bibliographic references (notably ISO 5855‑3 and ISO 7320).

Practical applications

• Protection of hydraulic, pneumatic and fuel system ports on aircraft during manufacture, shipment and storage.
• Standardizing cap and plug dimensions for suppliers of protective components to ensure interchangeability and correct seating without damaging threads or seals.
• Use by quality engineers, procurement and supply chain teams to specify correct protective devices on purchase orders and maintenance procedures.
• Helpful for designers creating packaging, transport fixtures, or MRO (maintenance, repair and overhaul) workkits that require reliable contamination control.

Who should use ISO 9634:1994

• Aerospace OEMs and tier suppliers that manufacture or finish fluid‑system components.
• Cap and plug manufacturers seeking compliance and interoperability with aerospace fittings.
• Maintenance organizations and logistics teams that require standard protection practices for fluid-system components.
• Engineering and quality assurance personnel specifying protection requirements in technical data packages.

Related standards

• ISO 5855‑3 (MJ thread series limits)
• ISO 7320 (threaded, leak‑tight fluid connectors)

Keywords: ISO 9634:1994, aerospace fluid systems, plastic protective caps, plugs, dimensions, MJ thread, protective devices, transit and storage protection.