thruaxle

A thru-axle, or through-axle, is a bicycle wheel fastener that passes completely through the frame dropout and the wheel hub, and is secured by threaded ends. The design replaces the traditional quick-release skewer and is used on many modern road, gravel, and mountain bikes. By clamping the wheel directly to the frame, a thru-axle increases tuning accuracy, lateral stiffness, and brake-disc alignment, contributing to better suspension performance and wheel tracking.

Common standards and sizes vary by application. Front thru-axles are typically 15 mm in diameter, with widths such as 100 mm for standard road frames and 110 mm for Boost-equipped frames. Rear thru-axles are usually 12 mm in diameter, with widths including 142 mm (non-Boost) and 148 mm (Boost). There are older or niche configurations, such as 12x135, but 12x142 and 12x148 are the dominant rear formats today. The exact axle length and end-cap design must match the frame, hub, and dropout spacing, and many frames support conversion through different end caps or adapters.

Advantages of thru-axles include improved wheel stiffness and alignment, easier, more repeatable wheel changes, and reliable disc brake rotor positioning. They also allow wider hubs and more robust brake engagement on high-load applications. Potential drawbacks are added weight, the need for specific axle parts, and the requirement that frames and hubs are designed for the corresponding standards. Maintenance involves keeping the threads clean and torquing the axle to the manufacturer’s specification.