thruaxles

Thru-axle is a bicycle wheel fastener used on frames and forks with disc brakes. It consists of a large-diameter axle that passes through the hub and the dropouts, securing the wheel with a single through-axle rather than a traditional quick-release skewer. The ends are threaded or use end caps that clamp when the axle is tightened with a lever or bolt, providing increased stiffness and precise alignment.

Common sizes vary by region and discipline. Front through-axles are typically 12x100 mm, with some forks using 15x100 mm. Rear through-axles are commonly 12x142 mm, with wider standards such as Boost 12x148 mm and downhill variants like 12x157 mm used on certain frames. The diameter is usually 12 mm for most modern mountain and road applications, but the length and end-cap design differ.

In terms of construction, thru-axles are often made from aluminum or steel, with end caps and threads designating compatibility with specific frames and hubs. They pass completely through the hub barrel and fork or frame, and are tightened to a specified torque. Some systems use compatible end caps to adapt the same hub to different frame standards.

Compatibility is a key consideration. Thru-axles require hubs, frames, and forks that share the same standard. They are not universally interchangeable across all frames. Some hubs and frames permit end-cap swaps or adapters to join different standards, but compatibility must be verified. Improper fit or under- or over-torquing can compromise wheel retention or safety.

Advantages of thru-axles include increased lateral stiffness, accurate rotor alignment, and secure wheel retention under heavy braking and rough terrain. Disadvantages can include added weight, greater installation effort, and the need for matching components and torque specifications.