WHAT THIS IS

How the answer is derived

The usual approach is a hand-maintained list of which part works with which. That collapses as the catalogue grows — a thousand parts is roughly half a million pairs, and nobody keeps that current.

Instead, every part here records the standards of its interfaces. A stem declares what it clamps onto (say, a 1 inch quill) and what it clamps around (25.4mm bars). Compatibility falls out of comparing those.

Which is why every stem that fits a 1 inch threaded steerer is a query result, not a list somebody typed. Add one part and every affected listing updates.

Five verdicts, and one of them is "unknown"

Being able to answer "unknown" is the whole premise. Guessing "probably fits" is easy, and the moment we do it, every other verdict on the site stops being worth anything.

Where several interfaces are involved, the worst verdict is the overall verdict. One unknown makes the whole answer unknown. We do not round that up to "yes, with a caveat".

Sources

Every standard, part and brand record carries at least one source URL. A record without one fails the build. That gate exists so an unsourced claim cannot ship, and it is not the sort of thing you can add later — so it went in first.

Sources are listed at the foot of each page, and confidence is shown as one of three levels: verified against a source, likely but wanting a primary document, or unverified. Where something is unverified, it says so.

What this site refuses to do

• No prices, no stock levels. Used listings are search links only. Pulling prices in and displaying them here is outside what those services permit.
• No scraping. There is no pipeline that harvests other people's data.
• No structured data that misstates what a page is. Marking parts up as Products would earn richer search results; we sell nothing and quote no prices, so we don't.
• No borrowed photography. The drawing on the front page is ours. We are not going to manufacture atmosphere out of pictures we did not take.

Coverage, and its limits

This is nowhere near complete and is still being added to. You will hit parts we do not carry and combinations that come back "unknown". That means we have not looked it up yet — not that it does not fit.

Languages

Published in English and Japanese. Japan is a primary source of track components, and some of that information exists only in Japanese. Carrying it into English is a large part of why this site is written in both.