Lug wrench

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Lug wrench is the U.S. name for a type of socket wrench used to turn lug nuts on automobile wheels. In the UK it is commonly known as a wheel brace or wheel wrench.

The form commonly found in car trunks is an L-shaped metal rod with a socket wrench on the bent end and a prying tip on the other. The prying tip is mainly intended to remove hub caps or wheel covers that may be covering a wheel's lug nuts. Another common type (sometimes known as a spider) is made in the shape of a cross, with different sized sockets on each of the four ends.

Ideally, the nuts (or bolts) should be tightened with a torque wrench. Lug wrenches are much less expensive because they lack the ability to measure or limit the force used. Installing a wheel with a lug wrench thus requires a bit of rough guessing about proper tightness. Excessive force can strip threads or make the nuts very difficult to remove. Also, uneven torque between the various lug nuts, or excessive torque, can lead to warping of the brake rotor if the car is equipped with disc brakes. (For this reason (excessive torque), impact wrenches should properly be used only for removing lug nuts, not for tightening them, although in practice this rule is often ignored for convenience's sake, even by professional mechanics.)

When re-fitting a wheel, always tighten the nuts (or bolts) in a criss-cross pattern (to even out the forces) and start with only 'finger tight' on all nuts. In this context 'finger tight' is tight enough to reach the point where free play is taken up and proper tightening is about to begin, say, the tightening force using the lug wrench/wheel brace like a screwdriver. Repeat this perhaps twice, to ensure the wheel is properly centred and restrained by all nuts (as often the first nut(s) you tightened will be slightly loose after completing the set for the first time), then lower the wheel to the ground and repeat the criss-cross tightening pattern to modest torque (say few fingers force on the lug wrench/wheel brace arm), then finally repeat the sequence to full hand force.

Rarely, and more often with large trucks and lorries, insufficient force can lead to the nuts coming undone while in use. Because of this, it is best to use a torque wrench or similar tool to finally tighten the wheel lug nuts to the proper torque specification as soon as possible after using a lug wrench to affix a wheel. At the very least, you should check the tightness after 50-100km/miles when things have been subject to some vibration and thermal cycling.

Lug wrenches are known for their use as weapons in cases such as road rage, (often called the classic southern weapon, in the southern region of the United States) as they are readily available in most cars, made of metal and heavy enough to cause injury. They are also increasingly referred to as tire irons, due to the relative rarity of the tire iron, another metal tool of similar size which is not needed on modern tubeless automobile tires and so has not been in common use for several decades.