All About Thru Axles

As a method of securing wheels to frames and forks, thru axles are superior in concept but muddled in execution by the inability of the bicycle industry to settle on a common standard. Thru axles can dramatically increase the stiffness of the interface between the hub and dropouts, while giving the hub a very specific mounting position to improve the interface between caliper and rotor on disc brake equipped bikes. However, between front and rear standards, axle thread pitch and diameter, and a dizzying array of dropout widths, there are dozens of standards to weed through. And, unfortunately, there aren’t many places to find good answers to compatibility questions; most frame manufacturers don’t even publish the standards that they use. In the event that you lose your stock axle or wish to upgrade, this lack of information can be frustrating to say the least. It is our hope with this article to shed a little light on the issue.

A Common Misconception:  DT Swiss manufactures thru axles for just about every variant, so don’t expect that just because your current thru axle has a DT logo it uses a DT standard. Chances are it’s some other variant developed or chosen by the frame manufacturer with a stock axle that was merely manufactured by DT Swiss.

The E-thru Conundrum:  “E-Thru” is a Shimano-developed standard, with several variants sharing the E-Thru name. Fits are based on dropout thickness and use of internal threading or an external, replaceable nut. For example, a standard E-Thru 142 axle also fits on many E-Thru Boost 148 frames, while the standard E-Thru axle may be too long for many E-thru 142 frames because they require a shorter version. If possible, we strongly recommend using actual length measurements taken from your existing E-Thru axle when ordering a replacement. Don’t assume that because your frame is Boost 148 and uses E-Thru that it requires the E-Thru Boost 148 axle, as often it may not.

Sizing:  There are 4 main attributes to consider when determining the proper thru axle standard for your bike:

Bolt Head Interface: Flat or conical
Total Length: The length of the axle, not including the head.
Thread Length: The length of the axle’s threaded portion.
Thread pitch: Thread standard used on the axle, expressed as distance between threads in millimeters.
Fits: An list of known compatible forks or frames, by no means comprehensive.
Important Note: There can exist small variations within each standard. In general, any model within the listed variant should work for your application with few exceptions.