What is a Through Axle? Types and How to Choose

What is a Thru Axle?

A thru axle is a type of shaft that passes through the wheel hub to secure the wheel to the frame or fork.

Until recently, quick-release skewers were the mainstream method for securing wheels. However, with the growing popularity of disc brakes in recent years, thru axles—which offer greater clamping force and rigidity—are increasingly being used for disc brake wheels.

Advantages of Thru Axles

There are two main reasons why thru axles are used with disc wheels:

1. Strong resistance to lateral forces due to threaded mounting
2. The disc rotor aligns in the exact same position every time

Quick-release systems secure the wheel by clamping from both sides, whereas thru axles are threaded or use dedicated mechanisms for attachment. This provides stronger fastening and better resistance to lateral flex.

Unlike rim brakes that clamp the outer edge of the wheel (the rim), disc brakes apply force at the hub using a rotor. This places higher demands on the hub’s rigidity, which thru axles can fulfill.

Another major advantage is the consistent positioning of the disc rotor thanks to the threaded engagement. Since disc brakes work by clamping a rotor between brake pads, even a slight misalignment can lead to reduced braking performance or noise.

Quick releases can introduce minor inconsistencies depending on how they’re tightened, but with a thru axle, the wheel is fixed in exactly the same position every time, minimizing the risk of rotor misalignment.

Disadvantages of Thru Axles

The main disadvantage of thru axles is that they require dedicated frames and wheels. This means that most parts compatible with quick releases cannot be reused, which may be a downside for riders with existing components.

Some people also say, “Thru axles are harder to tighten or more troublesome than quick releases,” but after a few uses, it becomes easy to handle. Once you’re used to it, the benefit of always fastening at the same precise point outweighs the initial inconvenience.

In most cases, this perceived disadvantage is minimal.

How to Remove a Thru Axle

With quick-release skewers, removal was as simple as opening the lever and unscrewing it. Thru axles, on the other hand, are removed by turning them with a tool such as an Allen key.

You might think, “Isn’t it a hassle to carry an Allen key just to remove the axle?” However, most thru axles come with a lever-shaped built-in handle. This is typically left in place during rides and only used when removing the axle, so it’s not an inconvenience in practice.

Can You Convert a Quick Release Bike to Thru Axle?

Generally, it’s not possible to convert a quick-release sports bike to use a thru axle.

There are two main reasons for this:

1. The frame and fork dropouts don’t have threading for thru axles.
2. The rear dropout spacing is different.

Thru axles don’t just clamp the wheel—they are threaded into the frame or fork using dedicated mechanisms. If your bike’s frame or fork lacks this threading, you can’t securely install a thru axle. Most quick-release frames use open dropouts (slots) without threads.

Additionally, the standard spacing for road bikes is different:

• Thru axle: 100 mm front, 142 mm rear
• Quick release: 100 mm front, 130 mm rear

Because of this mismatch in rear spacing, conversion is usually not feasible.

Thru Axle Standards and Types

Differences in Axle Diameter

Thru axles come in different diameters.
For road bikes, 12mm is the standard. Mountain bikes (MTBs) also often use 12mm, though some models use thicker 15mm axles. Bikes that require higher rigidity may even adopt 20mm axles.

The axle diameter must match the threading on the frame or fork, as well as the hub axle hole size.

Some wheels are compatible with different thru axle sizes through the use of adapters.

Differences in End Width (OLD)

As explained earlier, road bikes typically use 100mm front and 142mm rear spacing for thru axles.
MTBs often use 110mm front spacing, with 142mm still common for the rear. However, older MTB models may use 135mm, and some Specialized models use a proprietary 142+ spacing. There’s also the Boost standard, which has a 148mm rear width.

Axle length varies depending on the bike’s design. It’s important to check specifications carefully when replacing or customizing parts, as axle length will affect compatibility.

Differences in Axle Length

Axle length refers to the total shaft length. Since the frame has some thickness, the axle must be longer than the frame’s dropout width.

However, since the thickness of the frame dropouts varies by manufacturer, an axle that’s too long can leave a gap between the shaft and the frame. Conversely, a short axle may not thread in fully.

Therefore, be sure to check axle length when selecting a thru axle.

Thread Length

Thru axles are male-threaded. The thread length must be long enough to reach the full depth of the corresponding female thread in the frame or fork. If the threads are too short, the axle cannot be tightened properly.

Differences in Mounting Method

Most thru axles are mounted by threading into the frame or fork.
However, there are unique systems like the R.A.T. (Rapid Axle Technology) developed by Focus and used in some Merida bikes.

Naturally, such specialized systems require matching frames, forks, and axle designs.

Differences in Thread Pitch

Even among threaded thru axles, thread pitch (the distance between threads) can vary. Common pitches include 1.0mm, 1.5mm, 1.75mm, and 2.0mm.

Some bikes even use different pitches for the front and rear axles.
While axle replacement usually means matching the original spec, in some cases you can change the frame’s receiving hardware to accommodate a different standard.

How to Choose a Thru Axle

As we’ve seen, when choosing a thru axle, you’ll need to consider:

1. Axle length
2. Axle diameter
3. Mounting method (threaded, proprietary, etc.)
4. Thread pitch
5. Thread length

Thru axle specifications are often printed directly on the axle itself. By checking this, you can identify compatible replacements for your bike.

The image above shows a Shimano thru axle (AX-MT700), which lists:

1. 142x12 (compatible OLD spacing)
2. M12 x P1.5 (compatible threading standard)
3. Length 166 (overall axle length)

If both the end spacing and thread specs are correct, the axle will generally fit. However, if the axle is too long or short, or if the thread length is incorrect, it may not secure properly.

In the thread spec “M00,” the number after M represents diameter, and after P is the pitch. Even if diameter and length match, an incompatible pitch will prevent the axle from threading correctly.

When shopping online for replacement axles, always confirm the printed specs on your current axle to ensure compatibility.