The same bearing can sell for £8, £19 or £42 depending on the box it arrives in. Sometimes those are three different products; sometimes it is the same one with three margins. Knowing how to read the difference is the heart of buying parts.
Four categories circulate, and they are almost never distinguishable from a listing photo.
The four categories
1. The manufacturer's original part (OEM in the strict sense). Sold through the dealer network, in the vehicle brand's packaging, carrying the manufacturer's part number. The manufacturer almost never makes it in-house: it has it produced by a supplier to its own specification.
2. The OE-supplier part (OES). That same supplier sells the same part, often off the same production line, under its own brand and its own part number. Bearings, seals, filters, pads, plugs, chains: in most cases it is strictly the same product. The price gap runs from 20 to 40 %.
The one detail that can differ: some parts are produced in two grades, one for factory assembly and one for the spares channel. It is rare, but it is the point to check on critical components.
3. The aftermarket part. Designed by a third party to fit the vehicle, with no link to the original supplier. The best and the worst live side by side here. Some specialist makers beat the original on specific points. Others respect the interface dimension and nothing else: different material, missing treatment, loose tolerances.
4. The counterfeit. A copy that usurps the brand and packaging of one of the three categories above. It is not a cheap part: it is a part that lies about what it is.
Reading a part number
It is the only reliable anchor. A complete manufacturer part number — as it appears on the exploded diagram for the model, model year and variant — buys you three things:
- Comparing offers that genuinely cover the same article.
- Tracing the supplier, and therefore the equivalent OES reference.
- Spotting supersessions: a number replaced by another signals a change to the part, often a fix for a known fault. The most recent version is usually the right one.
Beware partial numbers. Plenty of listings show a fragment of a reference, or a "compatible with" claim without saying which. On parts with variants — pads, bearings, oil seals, chain kits — the fragment is not enough: two model years of the same machine can take different parts.
The counterfeit signals
Before you pay:
- A price that has broken away, of the order of 60 to 80 % below the market, on a brand that does not discount.
- A seller with no complete part number, describing by vehicle model rather than by the part.
- Generic or reused photos, with no shot of the actual product and its markings.
- Approximate packaging: off-centre logo, different typeface, a barcode that matches nothing, no batch number.
On delivery:
- Weight. A counterfeit pad, disc or sprocket is almost always lighter, through missing material or missing treatment. Kitchen scales are enough to compare with the part you removed.
- Stamped markings. Original parts carry a clean stamp, often with a production code. A blurred laser etch or an inked stamp is suspect.
- Machining. Burrs, uneven chamfers, threads that snag: on a modern industrial part, these are defects that do not get through inspection.
- No documentation: no instructions, no torque figure, no approval marking where one is mandatory.
