How the numbering systems actually work, why a cross-reference alone is not enough for hydraulics, and a five-minute check that prevents most wrong-part returns.
Hydraulics are the category where cross-referencing goes wrong most often, because two cylinders can share a bore, a port thread and a car model and still not fit each other's vehicle.
The three numbering systems
- The OE number is issued by the vehicle manufacturer. It is the most reliable identifier, and it is what the customer reads off the old part.
- The aftermarket reference is the number a brand like TRW, LPR, Metelli or A.B.S. assigns to its equivalent. One OE number often maps to several aftermarket references, and one reference can cover several OE numbers.
- TecDoc-style catalogue data links OE numbers, aftermarket references and vehicle applications together. It is the industry's shared lookup, and it is what a serious supplier searches before quoting.
Why a cross-reference alone is not enough
A cross-reference tells you two parts are equivalent in the catalogue. It does not tell you that the bore is the same, that the port thread is the same, or that the reservoir interface matches. For friction material the catalogue mapping is close to sufficient; for a hydraulic cylinder it is only the beginning. That is why we confirm the bore, the port and the mounting distance in writing, against a drawing, on every quotation.
The five-minute check
- Read the number off the old part itself, not from a workshop invoice.
- Write down the vehicle's year, engine code and transmission type.
- Photograph the cylinder from three angles, including the port and the mounting flange.
- Put a steel rule across the bore so the scale is visible in the photo.
- Send all four items together — not one at a time. It saves a full day of back-and-forth.
Do this and the wrong-part return rate drops to near zero, which matters more to your margin than any price negotiation on the container.