lockring

A lockring is a ring-shaped fastener that secures a component in place by engaging threads or notches, creating a fixed relationship that resists loosening from vibration and torque. Lockrings are used in a variety of mechanical assemblies, but are especially common in bicycles, where they help maintain correct preload and keep sprockets or bearings from shifting.

In bicycles, there are two principal applications. The first is the bottom bracket, where the left-side lockring threads onto the bottom bracket shell to lock the adjustable cup in position. Tightening the lockring against the adjustable cup sets the bearing preload and prevents the cup from moving during riding. This type of lockring usually has notches or splines and is removed and installed with a dedicated lockring tool or hook/spanner.

The second major use is with cassettes or freewheels on the rear wheel. A cassette lockring threads onto the freehub body and clamps the stack of sprockets in place. A lockring tool with compatible splines is used to tighten or loosen it, typically by turning clockwise to tighten and counterclockwise to loosen.

Lockrings are typically made from steel or aluminum and are designed to engage securely with the mating component. Proper installation requires using the correct tool and avoiding overtightening, which can damage threads or the lockring itself. If a lockring is damaged or worn, it should be replaced to preserve proper adjustment and safety.