The Strongest Link: Technical Guide to UIC Leaflet 826 (Screw Couplings)

What is UIC Leaflet 826?

UIC Leaflet 826, formally titled “Technical specification for the supply of screw couplings for tractive and trailing stock,” is a critical document issued by the International Union of Railways (UIC). It defines the strict manufacturing and testing standards for the manual coupling systems used on the majority of European freight and passenger trains.

A Screw Coupling is the mechanical link that connects two railway vehicles, transmitting the pulling (tractive) forces. Because a failure in this component could lead to a train parting (breakaway), UIC 826 mandates rigorous quality control for materials and assembly. The standard applies to both Tractive Stock (locomotives) and Trailing Stock (wagons and coaches).

Key Technical Requirements

The leaflet outlines the “conditions of supply,” which serves as a contract between the railway operator and the manufacturer. Key areas include:

• Material Composition: The steel used must possess high tensile strength and ductility to withstand sudden shocks without snapping.
• Mechanical Testing: Every batch must undergo destructive and non-destructive testing, including tensile tests to verify the Breaking Load (typically 850 kN or 1350 kN depending on the class).
• Dimensional Tolerances: Precise measurements for the thread of the screw and the geometry of the shackle are enforced to ensure Interoperability between vehicles from different countries.

Comparison: UIC 826 vs. EN 15566

While UIC 826 is the global reference, the European Norm (EN) standard has harmonized these requirements for the EU market.

Components of a Screw Coupling

The assembly defined in UIC 826 is not just a simple chain. It is a complex mechanism consisting of:

• The Shackle: The loop that goes over the draw hook of the opposing vehicle.
• The Screw: A threaded shaft that allows the coupling to be tightened (shortened) to compress the buffers, reducing slack.
• The Weighted Lever: A handle with a ball weight that allows the shunter to tighten the screw manually and keeps it from loosening due to vibration.