I have an On One - Bish Bash Bosh (Gravel Bike) and just built some nice road tyres for summer.

The bike takes a 15mm thru axle front wheel and a 12mm thru axle rear wheel

Sadly the wheels I built have 12mm thru axles front and rear

I have a 12mm thru axle to use with the front wheel and my question is:

Is there an adapter that I can use to make the 12mm front hub and axle fit with a 15mm fork?

The wheels are DT Swiss 470db and the front hub is a SCS 722 r.e



4 Answers 4


There's not a generic part that does what you want it to do here.

Thru-axles are part of the structure of a frame or fork. Even if it wouldn't really matter in most cases, making a generic aftermarket thru axle that steps down to a smaller-than-designed diameter like one can imagine would be asking for trouble.

When this kind of conversion is possible with off the shelf parts, it's typically done via hub-specific endcaps. They have to be hub-specific for the sealing elements to work. Good 12x100 hubs aren't necessarily convertible to 15, because to do so implies a design that's much bulkier than a road hub necessarily needs to be.

Specialized has made a lot of spare parts for their stuff over the years, and finding an amenable dealer to look through the catalog to make sure there's nothing available for your hub is probably the first step here, and one that nobody here can conclusively do for you unless they happen to be a dealer.

You can also pull an endcap and see whether it's one of the many 12x100 front hubs with a 15mm ID bearing such as 6902. I'm not totally sure of all the design reasons for this, but there are very few convertible hub designs that put the thru-axle in direct contact with the main bearings. There are a few exceptions I've seen to that pattern but it's pretty prevalent, so if they're 15mm ID it's a pretty good bet there aren't commercial endcaps that just do what you want. What would go wrong by boring out the ones you had were that the case is a separate question.


While it's not a common problem, there are companies like JJBP that make the specific kit you would need, that consist of frame inserts and a correct length through axle. The kits tend to be specific to application though I imagine that this is to aid marketing to a certain extent as there are only so many possible variations.

See: https://www.ebay.co.uk/sch/i.html?_from=R40&_trksid=p2047675.m570.l1313&_nkw=JJBP+15mm+12mm&_sacat=0

It's not the cheapest solution, but if your hub cannot be adapted to 15mm by changing the end caps (many can!) then this is one professionally made solution.


Essentially you're trying to make a 15mm shaft fit through a 12mm hole.

Adapters won't do it, you need a replacement through-axle for your specific frame. Even then, the axle has to fit a 15mm hole on the far side too, so you're looking at either a reducing bushing (15->12mm) on the far side, or a custom two-part through axle.

Might be time to stop throwing good money after bad, and buy the correct front wheel hub. With luck, you can get the same brand with the same measurements, and just re-lace the wheel onto the right hub.

Another option is to replace your fork, but that's going to be a significant cost. Sorry, there are no good options for you, and your frame manufacturer is the next point of contact.


Thanks everyone for answering and I think the smartest option is to rebuild the wheel with a 15mm hub.

JJBP looks like the best option but the price is a little challenging.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.