Short answer: an axle is described by three numbers — diameter, hub width, and thread pitch. A "12x142" axle from one bike will not necessarily thread into another 12x142 frame, because thread pitch and thread length are not standardised. For trainers, what matters is whether the trainer's end caps match your rear hub spacing, and whether your axle is long enough to reach through it.
Contents
- Quick release versus thru-axle
- Front axle standards
- Rear axle standards
- How to measure what you have
- Thread pitch: the trap
- Trainer compatibility
- Converting a hub between standards
- Common mistakes
- FAQ
Quick release versus thru-axle
A quick release skewer is a thin rod — usually 5mm — that passes through a hollow hub axle and clamps the wheel into open dropouts using a cam lever. The wheel is held by friction against the dropout faces.
A thru-axle is a much thicker rod — 12, 15 or 20mm — that threads directly into the frame or fork. The dropouts are closed holes rather than open slots. The axle becomes a structural part of the frame when tightened.
Disc brakes drove the change. A disc calliper applies braking force at the hub rather than the rim, which tries to pull the wheel down and out of an open dropout. Thru-axles remove that failure mode entirely and add useful stiffness at the same time.
Practically: if your dropouts are open slots you have QR. If they are closed holes you have thru-axle. There is no ambiguity once you look.
Front axle standards
| Standard | Diameter | Hub width | Typically found on |
|---|---|---|---|
| QR 100 | 9mm skewer | 100mm | Rim-brake road, older hybrids and MTB |
| 12x100 | 12mm | 100mm | Modern disc road and gravel |
| 15x100 | 15mm | 100mm | Older MTB, some gravel and cyclocross |
| 15x110 (Boost) | 15mm | 110mm | Modern mountain bikes |
| 20x110 | 20mm | 110mm | Downhill and heavy-duty forks |
The road and gravel world has largely settled on 12x100. Mountain biking has settled on 15x110 Boost. Most of the confusion sits with bikes from the transitional period, roughly 2014 to 2019, where 15x100 was common on gravel and cyclocross frames.
Rear axle standards
| Standard | Diameter | Hub width | Typically found on |
|---|---|---|---|
| QR 130 | 5mm skewer | 130mm | Rim-brake road |
| QR 135 | 5mm skewer | 135mm | MTB, hybrid, touring, some early disc road |
| 12x142 | 12mm | 142mm | Modern disc road, gravel, cross-country |
| 12x148 (Boost) | 12mm | 148mm | Modern mountain bikes |
| 12x157 (Super Boost) | 12mm | 157mm | Some enduro and downhill |
| 10x135 | 10mm | 135mm | Early thru-axle MTB. Uncommon now. |
12x142 is the modern road and gravel standard. If you bought a disc-brake road or gravel bike in the last few years, this is almost certainly what you have.
Note that 142 and 135 are closer than the numbers suggest — a 142mm thru-axle hub has 3.5mm end caps either side that locate into the frame, so the hub shell itself occupies the same 135mm. This is why some hubs convert between the two with a change of end caps.
How to measure what you have
Three measurements, all taken with the wheel out.
| Measurement | How |
|---|---|
| Hub width | Measure across the outside faces of the hub end caps — the surfaces that contact the frame. This gives 100, 110, 130, 135, 142, 148 or 157mm. |
| Axle diameter | Measure the axle rod itself, or the hole through the hub. 9, 12, 15 or 20mm. |
| Axle length | Measure the axle end to end, including the head. This is longer than the hub width because it passes through the frame on both sides. |
Write all three down before ordering anything. Two of the three is not enough.
Thread pitch: the trap
This is the part that catches people who have done everything else right.
Thru-axle threads are not standardised. Frame manufacturers chose their own, and three pitches are in common use on 12mm axles:
| Thread | Notes |
|---|---|
| M12 x 1.0 | Fine pitch. Common on road and gravel. |
| M12 x 1.5 | Coarse. Common on mountain frames. |
| M12 x 1.75 | Coarser still. Used by some manufacturers including certain Trek and Specialized frames. |
Two bikes can both be 12x142 and take completely different axles. On top of pitch, the threaded length varies — how far the thread runs from the tip — and so does the total axle length, because dropout thickness differs between frames.
The practical consequence: do not buy a replacement thru-axle on hub spacing alone. If you have lost yours, the reliable route is to order the axle specified by your frame manufacturer for your exact model and year. A generic "12x142 thru-axle" has perhaps a one-in-three chance of threading correctly.
If you are trying to identify an existing axle, a thread pitch gauge costs very little and removes the guesswork. Failing that, count threads across 10mm: roughly 10 threads means 1.0mm pitch, roughly 6-7 means 1.5mm.
Trainer compatibility
Direct-drive trainers — where the rear wheel comes off and the bike mounts onto the trainer's own cassette — need to match your rear hub spacing.
Most trainers ship with end caps or adapters covering the common standards, typically 130mm and 135mm QR plus 142mm and 148mm thru-axle. Check what is in the box before assuming.
Three things to get right:
- Spacing. The trainer's end caps must match your frame's rear spacing — 142 or 148 for thru-axle, 130 or 135 for QR.
- The axle itself. On a thru-axle bike you generally use your own axle, passed through the trainer. It has to be long enough to reach through the trainer body, and some trainers require a slightly longer axle than your frame's own. Several manufacturers sell a trainer-specific axle for this reason.
- Freehub body. The trainer has its own freehub, so it needs to match your cassette — see our freehub and cassette compatibility page. A trainer supplied with an HG body will not take a SRAM XDR cassette. Elite sell a SRAM XD/XDR freehub for their direct-drive units if you run SRAM AXS or Eagle.
Adapters by standard
| Your frame | Adapter |
|---|---|
| 12x148 Boost | Elite Knurled Boost 148x12mm |
| 135x10/12mm thru-axle | Elite 135x10/12mm or the knurled version |
| 10–12mm needing a spacer | Elite adaptor with spacer |
| Magene T110 / T200 | Magene thru-axle adapter kit |
Wheel-on trainers are simpler, because the wheel stays on and the trainer clamps the axle ends externally. If your bike is thru-axle you will need a QR-style skewer that fits the trainer's clamp — a 10mm E-Thru skewer covers this on classic trainers.
Setups that clamp the front fork are a separate case again. The Feedback Sports Omnium fork adapter handles 15x100 and 15x110 front axles, which the standard fitting does not cover. If you are adding a steering or gradient accessory such as the Elite Rizer, check its front-axle requirements separately — those clamp the fork and have their own adapter needs.
Converting a hub between standards
Many quality hubs convert between axle standards by swapping the end caps. The hub shell, bearings and freehub stay put; only the caps that interface with the frame change.
Common conversions that work on hubs designed for them:
- QR 135 ↔ 12x142 rear
- QR 100 ↔ 12x100 front
- 12x100 ↔ 15x100 front
- 12x142 ↔ 12x148 on some Boost-capable hubs
What you cannot do is convert a hub the manufacturer never designed for it, or change the hub shell width — a 135mm shell will not become a 148mm shell.
End caps are hub-model-specific, not brand-specific. Zipp, for instance, publishes different cap sets for Cognition, ZR1 and the 76/77 and 176/177 hub families, and they are not interchangeable between them. We carry sets including Cognition V2 rear 12x142, Cognition rear disc QR, ZR1 rear 12x142 XDR and several front sets.
Before ordering caps, confirm the exact hub model — it is usually printed on the hub shell.
Common mistakes
Ordering a thru-axle by hub spacing alone. 12x142 describes the wheel, not the axle. You also need thread pitch, thread length and total length.
Forcing an axle that won't thread smoothly. A thru-axle should thread in by hand for most of its travel. If it binds early, the pitch is wrong and continuing will damage the frame threads — which on a carbon frame is an expensive repair.
Confusing 15x100 with 12x100. Both are 100mm front hubs. The axle diameter differs and the hubs are not interchangeable without the correct end caps.
Assuming a trainer covers every standard. Most cover the common four, but Boost and Super Boost frames often need an additional adapter bought separately.
Over-tightening. A thru-axle is not a structural bolt to be cranked down. Most specify 10–15 Nm. Beyond that you risk the frame threads, not a better clamp.
FAQ
What is the difference between 12x142 and 12x148?
Hub width. 142mm is the road, gravel and cross-country standard; 148mm is Boost, used on modern mountain bikes to allow wider tyre clearance and a stronger wheel build. They are not interchangeable unless your hub is specifically designed to convert.
Can I put a thru-axle wheel in a quick release frame?
Not directly. Some hubs convert from thru-axle to QR by swapping end caps, if the manufacturer offers them for that hub. Without that, the answer is no.
Are all 12x142 thru-axles the same?
No, and this is the most common expensive mistake. Thread pitch varies between M12x1.0, M12x1.5 and M12x1.75, and thread length and total length vary too. Order the axle your frame manufacturer specifies for your model.
What thru-axle does my trainer need?
Usually your own bike's axle, passed through the trainer. Confirm your axle is long enough to reach through the trainer body — some trainers need a few millimetres more than the frame alone, and manufacturers sell longer trainer-specific axles for this.
How tight should a thru-axle be?
Most manufacturers specify 10 to 15 Nm. Check what is printed on your axle or in the frame manual. Hand-tight plus a firm nip is the practical version; a torque wrench is better.
How do I measure my hub spacing?
Take the wheel out and measure across the outside faces of the end caps — the surfaces that press against the frame. Not the axle, and not the hub shell.
My frame is 12x142 but the axle from my old bike won't thread in. Why?
Different thread pitch. Both frames are 12x142 in terms of wheel fitment, but the threads cut into the dropout differ between manufacturers. Stop before you damage the threads and get the correct axle for the frame.
Do I need a thru-axle for a wheel-on trainer?
No. Wheel-on trainers clamp the rear skewer or axle ends externally and usually ship with a suitable QR skewer. If your bike is thru-axle you may need a compatible skewer to replace it while on the trainer. Direct-drive trainers are where axle compatibility matters most.
Last updated: August 2026.
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Related: Freehub and cassette compatibility · Bottom bracket standards · Frame sizing by height and inseam