A lug nut or wheel nut is a fastener, specifically a nut, used to secure a wheel on a vehicle. Typically, lug nuts are found on automobiles, trucks (lorries), and other large vehicles using rubber tires.

The conical lug's taper is normally 60 degrees (although 45 degrees is common for wheels designed for racing applications), and is designed to help center the wheel accurately on the axle, and to reduce the tendency for the nut to loosen due to fretting induced precession, as the car is driven. One popular alternative to the conical lug seating design is the rounded, hemispherical, or ball seat. Automotive manufacturers such as Audi, BMW, and Honda use this design rather than a tapered seat, but the nut performs the same function. Older style (non-ferrous) alloy wheels use nuts with a 13 to 25 mm (1⁄2 to 1 in) cylindrical shank slipping into the wheel to center it and a washer that applies pressure to clamp the wheel to the axle.