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Conveniently enough, a lug wrench is a tool designed to loosen and tighten lug nuts. Lug nuts are responsible for keeping tire rims attached to the axles, which means they are usually kept very tight. Professional mechanics generally use pneumatic socket wrenches to accomplish this feat, guaranteeing that the lug nuts won't work themselves loose during normal driving. A lug wrench is designed to provide drivers with enough leverage to loosen lug nuts during a roadside emergency.
There are two common lug wrench designs drivers may encounter. One is a metal bar bent on the end nearest a socket wrench. The other common lug wrench configuration resembles a cross, with various socket wrenches on each arm.
Both provide enough leverage for a driver to loosen lug nuts, but many experts recommend the cross-shaped lug wrench for maximum leverage. The bent-arm lug wrench features a pry bar on the opposite end, however, which can make removing hub caps or other wheel covers much easier. Either type of lug wrench can be purchased in an auto supply or department store.
The lug wrench comes into play most often with a flat tire. The driver usually removes the spare tire, car jack and lug wrench from the trunk in order to replace the flat. Once the hubcap or wheel cover is pried off, the lug nuts are revealed.
The driver must loosen, but not remove, all of the lug nuts before jacking up the car. This involves placing the lug wrench over a lug nut and applying downward force until the nut breaks loose. Once the lug nut becomes loose enough to turn by hand, the driver repeats the process with the rest of the nuts. With a cross-shaped lug wrench, the driver should be able to apply both upward and downward pressure on the left and right arms. This additional torque is why many professionals prefer the cross-shaped lug wrench.
Great care must be taken not to strip out the socket of a lug wrench. If the end of a bent-arm lug wrench is not attached to the lug nut correctly, excessive force can damage the nut or the socket. A lug wrench made from softer metals may be less expensive than a drop-forged steel model, but it may not be able to handle the most stubborn lug nuts. It is not uncommon for car owners to replace the factory-provided lug wrench and car jack with higher quality tools from an auto supply store.