Overview
ISO 3842:2006 - Road vehicles - Fifth wheels - Interchangeability defines the dimensional characteristics required for mounting and interchangeability of fifth wheels on towing vehicles for semi-trailers. It covers both standard fifth wheels mounted on a mounting plate and direct-mounted fifth wheels fixed to the vehicle frame. The standard applies to fifth wheels intended to hitch semi‑trailers equipped with a 50 mm coupling pin (ISO 337) or a 90 mm coupling pin (ISO 4086). Test and strength requirements are referenced to ISO 8717.
Key topics and technical requirements
- Designation and coding: Identification format includes reference to ISO 3842, code (FW 50, FW 90, DFW 50), height class and width class for direct‑mounts.
- Mounting hole layouts: Specified fixing hole positions for mounting plates and subframes (figures in the standard).
- Bolt requirements:
- FW 50 (50 mm): minimum 8 bolts, M16, property class 8.8, symmetric placement.
- FW 90 (90 mm): minimum 12 bolts, M16, property class 8.8.
- DFW 50 direct‑mounted: minimum 12 bolts, M16, property class 8.8; OEM approval required.
- Height classes:
- Standard FW classes (H): 150, 170, 185, 205, 225, 250 mm (±5 mm).
- Direct‑mounted DFW classes (H): 150, 160, 175, 190, 225, 250 mm (±5 mm).
- Transversal widths (direct‑mounted):
- Class A W1 = 870 mm; subframe W2 = 860–880 mm.
- Class B W1 = 950 mm; subframe W2 = 940–960 mm.
- Inclination and alignment:
- Longitudinal inclination (uninstalled): minimum ±12° (±10° for DFW class 1).
- Maximum lateral angle: ±3° (see ISO 1726).
- Force introduction area: Defined top‑plate area (outer diameter D = 870 mm) where trailer forces must be applied; no holes or sharp edges allowed within this zone.
- Scope limits: Dimensions not specified may be chosen by the manufacturer; strength/test conditions referenced to ISO 8717.
Applications and users
- Vehicle OEMs and component manufacturers: design and produce interchangeable fifth wheels and mounting plates.
- Trailer and tractor designers: ensure compatibility between semi‑trailers and towing vehicles (50 mm / 90 mm kingpins).
- Fleet owners and maintenance shops: verify retrofit compatibility and correct mounting hardware.
- Testing laboratories and certification bodies: reference for dimensional compliance and interface checks.
- Aftermarket suppliers and engineers involved in fifth‑wheel installations and OEM approvals.
Related standards
- ISO 337 - 50 mm semi‑trailer kingpin dimensions
- ISO 4086 - 90 mm kingpin dimensions
- ISO 1726 - Mechanical coupling interchangeability between tractors and semi‑trailers
- ISO 8717 - Fifth wheel coupling strength tests
Keywords: ISO 3842, fifth wheel interchangeability, fifth wheel mounting, FW 50, FW 90, DFW 50, kingpin, ISO 337, ISO 4086, mounting plate, direct‑mounted fifth wheel.
