Drive and RestoreNOS, genuine, OEM, OES or aftermarket: what the parts labels really mean
Shop for parts for an older Fiat, Alfa Romeo or Lancia and you will see a handful of labels used as if they were interchangeable: NOS, genuine, OE, OEM, OES, aftermarket. They are not the same thing, and the difference matters for fit, quality, originality and price. Here is what each one actually means.
Genuine (OE): from the car maker
Genuine or OE (original equipment) parts come from the car maker itself, in the manufacturer’s packaging, with the manufacturer’s part number. It is what a dealer sells over the counter. You pay for the brand, but you also get the part the factory specified, made to its drawings and tested to its standards.
NOS: genuine parts that were never used
NOS stands for new old stock: genuine parts made during or shortly after the car’s production that were never fitted, and were kept in stock at a dealer, a distributor or the factory. For classic cars this is often the only way to buy a truly original part, because the manufacturer stopped making it decades ago.
What to know about NOS:
- It is new but old. Rubber, seals and hoses can harden on the shelf even if never used, so for those parts age and storage matter. Metal parts, trim, badges and electrical parts usually age much better.
- The original packaging and part number are part of the value, both for originality and for identifying exactly what you have.
- Supply is finite. When a NOS part is gone, it is gone.
OEM: the company that made it
OEM (original equipment manufacturer) is the most confusing term, because it is used in two ways. Strictly, it refers to a company that supplies parts to car makers for their production lines. In everyday use it is often stretched to mean “the same quality as original”, which is not the same thing at all.
OES: the original supplier, in its own box
OES (original equipment supplier) is the company that actually supplied that specific part to the factory, for example the brake caliper maker or the bearing manufacturer. Many OES companies also sell the same part under their own brand. That part can be identical to the genuine one, minus the car maker’s logo and box. Sometimes it is a cheaper second line, so it pays to know the supplier.
Aftermarket: made for the after-sales market
Aftermarket parts are made by companies for cars after they have been sold, not for the factory production line. Quality ranges from excellent to dreadful. Some aftermarket parts are direct replacements at a lower price and comparable quality. Others fit badly, or are copies of copies.
Which one should you choose?
| Situation | Best choice |
|---|---|
| Concours or originality-focused restoration | NOS or genuine, with the original part number |
| Safety-critical parts (brakes, steering, suspension joints) | Genuine, OES from the known supplier, or a reputable brand |
| Rubber and seals on a car you drive | Fresh genuine or OES; check the age of NOS rubber |
| Badges, trim, switches, electrical parts | NOS where originality matters; it ages well |
| Wear parts on a daily driver | Good OES or quality aftermarket |
Always start with the part number
Whatever you buy, the original part number is the key. It tells you exactly which version you need, lets you check supersessions, and lets you compare a NOS part, a genuine part and an OES part like-for-like. Our guide to finding part numbers in ePER explains how to find it.
For original and NOS parts for Fiat, Alfa Romeo and Lancia, specialists such as Italricambi stock parts by their original numbers.