By Maxxd · Published 21 September 2026
Three kinds of "other number"
Every part has more than one number, and customers search using all of them.
- Supersessions. The manufacturer replaced number A with number B (and later B with C). The old numbers are discontinued but still stamped on cars, printed in forum threads and quoted by garages. Supersession chains several links long are normal.
- OE cross-references. The vehicle manufacturer's original part number — the one on the dealer invoice — and its equivalents from aftermarket brands. A customer with a Ford number wants to know which Brembo, Pagid or Blue Print part replaces it.
- Competitor / interchange numbers. Other aftermarket brands' numbers for the equivalent part. Someone searching a Bosch number should find your equivalent from another brand, clearly labelled as such.
Treat them as different things in your data, because they are. A supersession is "this is the same part, renumbered". A cross-reference is "this part fits the same application as that one". The difference matters for returns and for honesty.
Why it's worth the effort
- Search intent. A part-number search is about as high-intent as a query gets. The person has the old part in their hand.
- Competition. Most parts sites don't handle old numbers. Being the site that does is a durable advantage.
- Returns. A customer who can confirm "your part replaces my old number" buys with confidence and sends fewer back.
- SEO. Old numbers accumulate links and mentions over years — owners' clubs, YouTube descriptions, workshop blogs. A live page for the old number inherits all of that.
How to store it
Alongside your product record, keep a table of aliases: one row per alternative number, with the number itself, its type (supersession / OE / interchange), the brand it belongs to, and, for supersessions, its position in the chain. Normalise numbers on the way in — strip spaces, dashes and dots, upper-case everything — and store both the normalised and display forms.
Supplier data will give you a start (TecDoc, and most manufacturers' catalogues, carry OE references and supersession data). It won't be complete. Your own returns and enquiries are the best source of the numbers customers actually search for — build a process to capture them.
How to search it
Part-number search on the site must match against all aliases, not just the primary SKU, and it must forgive formatting: "1K0 615 301 AA", "1K0615301AA" and "1k0-615-301-aa" are the same query. Then rank sensibly:
- Exact match on your current number
- Exact match on a supersession → show the current product with "replaces 1K0615301AA"
- Exact match on an OE or interchange number → show equivalents, labelled "equivalent to [brand] [number]"
- Prefix / partial match, for people typing the first few characters
Show why a result matched. "Your search 1K0615301AA was superseded by 5Q0615301F — here's that part" turns a confusing result into a confident one.
How to handle the URLs
When a part is superseded, don't delete the old product page. Either:
- 301 redirect the old URL to the new product, if the new product fully replaces it and there's nothing worth keeping on the old page; or
- Keep the old page live as a "discontinued — replaced by" page that links prominently to the new product, if the old number has meaningful search demand or links of its own. Mark it clearly, keep it indexable, and don't show a dead "add to basket".
Either way, the old number stays in the new product's aliases so on-site search still works. What you never do is let the old URL 404. That throws away the rankings and the links, and it tells Google your site is the wrong place to look for that number.
Showing it on the product page
A visible, crawlable "Part numbers" block on every product: your SKU, the manufacturer's number, the OE reference(s), the numbers it supersedes, and equivalents from other brands where you're confident of the interchange. Plain text in the page, not an image or a tab that only loads on click. This is what lets Google rank the page for the old number and what lets the customer confirm they've found the right thing.
Put the same data in your Google Shopping description and in eBay item specifics (OE/OEM part number is a standard field) — see Google Shopping fitment.
A word on honesty
Cross-referencing another brand's number is normal practice — the whole aftermarket runs on interchange data. But say "equivalent to" or "replaces", never present another brand's number as your product's own, and make sure the interchange is actually right. A wrong cross-reference is a return and a bad review with your name on it.
Part-number search, aliases and supersession handling are standard in every parts ecommerce build we do, and cleaning up the alias data is part of the fitment data work. The free fitment audit runs the forgiving-search test on your site for you.