Bike Wheel Axle Nut Size? (Must Know This)

Bike Wheel Axle Nut Size

Several factors like the bike’s frame and the axle’s size cause variation in the size of the wheel axle.

The wheel axle nut size varies greatly across different brand manufacturers. Sometimes, users customize their bikes which makes this variation have a greater margin.  

The regular wheel axle nut size on bikes is 15mm. It is common for sport and mountain bikes to find a nut size of 14 or 15mm. Bikes manufacturers usually give different nut sizes to the front and rear axles. Sometimes, the back axle will have a nut size of 15mm, and the front will go with a smaller value. 

What Size Nut is on the Back Wheel of a Bike?

Bike Wheel Axle Nut Size

The nut size on the bike’s back wheel often depends on the manufacturer of the bike.

Whatever nut size they decide to go with, there are a few common nut sizes in use by most bike manufacturers. 

The most common track nuts are 14 and 15-mm nut sizes. Your back tire is probably one of these two nut sizes.

It is not uncommon to have a front nut size of 14mm and a back nut size of 15mm.

Bikes made by popular brands use mm measurement. Brands that produce smaller axle sizes use 5mm or even 8mm.

15mm Bike Wheel Axle Nut 

Usually, mountain bikes have wheel axle nuts ranging between 15 to 17mm.

The 15mm wheel axle nut is a perfect fit for your bike if you are a mountain biker or general hiker. However, regular bikes can also have this nut size. 

Bike Front Wheel Nut Size

It all depends on which nut size your bike manufacturer decides to fit on your bike.

It is common to have a bike with a 14mm front wheel nut size and a 15mm back. It isn’t uncommon to have a 5mm or 8mm front wheel nut size. 

They are making the bike a lot more suitable for the task. Most times, bike manufacturers like to give a bike front tire a lesser nut size; hence, the back nut size has a larger size.

However, your front nut should be around 15mm or a few points less if you use a mountain bike

BMX Wheel Nut Size

BMX bikes are some of the simplest for off-road sport and qualify for stunts. BMX bikes are available in many models like dirt, street, and race bikes, only to mention a few.

These bikes have different sizes with different wheel axle sizes as well, which also applies to the wheel nut size.

Changing the wheel nut size of a BMX bike has a ripple effect; it also affects the size and height of the bike.

These bikes have various wheel sizes, with an average range of 12 to 24 inches. The most common within the range is 20 inches, which is more popular among people. 

Bike Axle Bolt Size

Bike axles have a standard rating these days, so you should see a 100mm long by 12mm wide thru-axle on the front axle of your bike.

There is some variation in the diameter. However, some bikes come with a 15mm diameter thru-axle. This variation depends on which manufacturer made the bike. 

The bolt size on the bike varies significantly as the thru axles’ size varies. A 142mm long axle with a 12mm diameter is most common on the rear thru-axle. But some bikes have thru-axles that are 135mm long. 

If you are unsure of the measurement of the bolts on your bike, you can always use a magnetic tape graduated in mm to calculate the bike’s axle bolt size.

Get a tape and stretch it across the bolt’s diameter, the flat side of the bolt. 

If the tape is a metric function, count the number of lines on the tape, and that’s your measurement.

For example, if you count eight lines on the tape, the bolt is 8mm. Repeat the same process to find any bolt size on the bike’s wheel axle. 

Curiosity might drive you to learn the measurement of your front thru-axle. If such a case arises, the thru-axle is measured inwardly towards the bike’s pitchfork.

For the rear thru-axle, the beginning point of measurement is from the heart and measured towards the frame, preferably at the dropouts. 

Frame nuts are also of different variations. You commonly see coarse Allen screws for bikes 4, 5, or 6mm.

Some bikes even use all three coarse Allen nuts on their bike frame. Most bikes use 5mm bolts, but 4mm and 6mm are also fairly common. 

What Threads Are Bike Axles?

Threads on bikes vary with their manufacturers. You can’t pick out a single thread as other threads are still frequently used. Some threads are also not commonly used by manufacturers.

Glace through the table below to better overview the various thread sizes used on an axle.

Axle TypeThread Size
Front Hubs (Quick Release)9mm X 1mm
Solid Axle⅜ in 26 TPI
Most Quick Release Rear Axles10mm X 1mm
Solid Rear Axle⅜ in 26 TPI

To ensure your and your bike’s safety, you must regularly check that the bike’s thread and axles aren’t loose or damaged.

If it’s not the bike’s thread size, it either won’t fit or will be loose. And this can lead to serious damage to the bike axle or even cause a serious injury to the rider.

For this reason, you can’t pick up any thread and fasten it to your bike. If you are more interested in knowing the threads on your bike’s axle, below are a few tips to help you do that: 

#1. Take the Bike’s Wheel to the Hardware Store

Hardware stores are always the best option as they have the measuring instruments to measure the thread size for your wheel.

Hardware store workers know everything regarding bolt and axle thread sizes, so they are always your best bet. 

However, even after enquiring from these professionals, you can always contact the hardware clerk if you still need some help getting the right thread size for your bike.

Any hardware clerk will immediately respond to your request and get you the exact thread size you need. 

#2. Read the Owner’s Manual

The manual is always a place to start as it comes with all the information you need on your bike. In this case, the thread size for the bike you have.

Get the owner’s manual and locate the page of the”bike axle thread size.”  These sets of pages have everything you need on the bike’s wheel axle and size.

Owner’s manuals usually aren’t given any attention, so you can always check online for an online copy if you misplaced the one that came with the bike. 

It’s unusual to hear an “M10” nut in the biking industry. Don’t be frightened; it is just a coarse 10mm diameter nut.

M10 x 25 is also fairly common. And since there’s no thread pitch listed, it is assumed to have a coarse thread. The 25m is just the length measurement. 

Bike axles are different between brands. Even bikes of the same brand have some variation in terms of thru-axles. 

Thru-axles vary this much because of the dropout design; the dropout design in many bike models varies.

The axle spacing can also cause a variation in axle size; even the slightest change in axle spacing gives an axle a different shape altogether.

These few factors, either together or on their own, can cause the variations you see in different bike axles.


Bikes are a fun thing to have. Whether you use it to commute or just for exercise, it would be of great help if you were knowledgeable in certain areas.

This basic knowledge could save you and your bike a trip to a local repair shop or the hospital.

Josh Matthews

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