ISO 4038:1996

Overview

ISO 4038:1996 specifies essential dimensions and physical characteristics for metallic pipes and fittings used in hydraulic braking systems for road vehicles. The third edition (1996) updates and replaces the 1984 edition and covers single-flare pipes, tapped holes for cone sealing, male fittings, and hose end fittings used in brake fluid circuits. The standard ensures interchangeability, safety and corrosion resistance for brake tubing and connectors.

Key topics and technical requirements

• Scope and materials: Applies to double-walled rolled metallic tubes and compatible coated tubes for use in vehicle hydraulic brakes.
• Dimensional specifications: Detailed dimensions for bare pipe diameters, wall thicknesses, single flares and flange geometries are given in tables and figures to ensure mating compatibility.
• Tapped holes (cone sealing): Defines tapped-hole geometries and optional hole entry forms for reliable cone-type sealing of fittings.
• Male fittings and hose end fittings: Drawings and dimension tables for male fittings and both male/female hose end fittings; throat, hex sizes and sealing faces are specified.
• Mechanical and surface requirements: The standard lists mechanical characteristics for steel tubes (tensile strength, yield point, elongation, hardness) and requires inner/outer surfaces free from oxidation. The outer surface must be corrosion-protected and withstand the NSS salt spray test in accordance with ISO 9227 for at least 96 h.
• Assembly torques: Minimum tightening torques are specified (for example, 30 N·m for certain M10/M12 fittings, 35 N·m for larger fittings and hose end fittings) to ensure secure connections.
• Compatibility: Pipes with additional plastic coating are permitted provided they remain compatible with the specified fittings, tapped holes and flares.

Applications and who uses this standard

ISO 4038 is used by:

• Automotive OEMs and tier-1 brake system suppliers for part design and specification.
• Manufacturers of brake pipes, fittings and hose assemblies to ensure interchangeability and safety.
• Component and materials engineers for selection of tubing and surface treatments.
• Quality, testing and certification labs for acceptance testing (dimensional, mechanical, corrosion).
• Maintenance, repair and aftermarket producers to match replacement parts to original specifications.

Practical applications include design/manufacture of brake lines, production control, supplier specifications, and ensuring reliable cone-sealed connections in hydraulic brake circuits.

Related standards

• ISO 9227:1990 - Corrosion tests in artificial atmospheres (salt spray tests) - referenced for corrosion resistance.
• Referenced/related ISO documents on brake hose assemblies and double flare fittings where noted (see ISO bibliographic references in Annex A).

Keywords: ISO 4038, hydraulic braking systems, road vehicles, brake pipe fittings, single flare, male fittings, hose end fittings, tapped holes, cone sealing, brake line dimensions.