ThroughAxle

Through-axle, or thru-axle, is a bicycle axle that passes completely through the hub and the fork or frame dropout. The wheel is secured by threading on the ends of the axle into the frame or fork, replacing the traditional quick-release skewer. This design provides a fixed, centered connection and is common on bikes equipped with disc brakes.

Construction and operation: The axle is hollow, allowing the wheel to slide onto the hub while the ends are threaded or fitted with end caps that mate with the dropout. Installation is performed by threading the axle ends or engaging a clamping lever and tightening to the specified torque. The result is improved wheel alignment, reduced lateral flex, and more precise brake alignment, particularly under heavy braking or rough terrain.

Sizes and compatibility: Through-axles come in several diameters, most commonly 12 mm or 15 mm. Front through-axles are typically 12x100 mm, 12x110 mm (boost), or 15x100/15x110 mm depending on the frame. Rear through-axles are commonly 12x142 mm (standard) or 12x148 mm (boost). Thread pitches vary by manufacturer, with common examples including M12x1.0 and M12x1.5. Compatibility requires frame dropouts, hubs, and end caps that match these dimensions and standards.

Advantages and limitations: The primary advantages are increased stiffness, better wheel alignment, and improved handling under braking. They reduce dropout flex compared with quick-release systems. Limitations include greater weight, the need for compatible hubs and frames, and the tool requirement for installation and removal. Some riders find through-axles less convenient for rapid wheel changes on the road or while traveling.