ISO 4039-2:1998

Overview

ISO 4039-2:1998 specifies essential dimensions and material/surface requirements for pipes, male fittings and tapped holes with conical sealing surfaces used in road-vehicle pneumatic braking systems. It applies to the metric series of metallic and thermoplastic tubing and associated fittings for compressed-air brake circuits operating below 2 MPa (20 bar).

Key topics and requirements

• Scope: Metric-series pipes, male fittings and tapped holes with conical sealing surfaces for pneumatic brakes on road vehicles (pressure < 2 MPa).
• Materials: Permitted materials include metals (examples: steel, copper, copper alloys) and thermoplastics (example: polyamide).
• Pipe sizes: External diameters specified include 6, 8, 10, 12, 14, 15, 16, 18, 20 mm (see standard tables for detailed combinations with thread sizes).
• Threaded fittings and ports: Detailed dimensional tables specify tapped-hole and male-fitting geometry, thread sizes and engagement depths to ensure reliable conical sealing.
• Sealing details: Conical sealing surfaces and O‑ring groove dimensions are defined; O‑rings are normally specified with a minimum hardness of 70 IRHD unless otherwise stated. The cone angle and groove requirements align with, but are more stringent than, ISO 6149 to meet braking-system sealing demands.
• Surface condition and corrosion protection: Inner and outer pipe surfaces must be free from oxidation, smooth and clean. External corrosion resistance must be demonstrated by agreed test methods per ISO 9227 (salt spray), with a minimum 200 h exposure recommended.
• Informative annexes: Annex A explains the relationship to ISO 6149 and gives a recommended identification statement for conformity:
  "Tapped holes with a conical sealing surface conforming to ISO 4039-2:1998, Road vehicles - Pneumatic braking systems - Part 2: Pipes, male fittings and tapped holes with conical sealing surface."

Applications and who uses it

ISO 4039-2 is used by:

• OEMs and chassis manufacturers designing pneumatic brake circuits.
• Component suppliers producing tubes, male fittings, ports and lock-nuts for braking systems.
• Quality and testing laboratories verifying dimensional conformity, sealing and corrosion resistance.
• Procurement and aftermarket teams ensuring interchangeability and compatibility of fittings across suppliers.
• Regulatory bodies and certification authorities reviewing compliance for vehicle safety standards.

Practical applications include component design, production tolerancing, supplier specifications, assembly guidelines and maintenance/replacement part matching to ensure leak-free, durable pneumatic brake connections.

Related standards

• ISO 6149 (parts 1–3) - connections for fluid power and general use (reference for cone/O‑ring geometry).
• ISO 9227:1990 - salt spray corrosion testing (normative reference used for corrosion resistance assessment).