Here's a part of your vehicle you probably don't think about much: lug nuts. They're what fasten your wheels onto your axles. Pretty important, right? In order to take the wheels off your vehicle to service the brakes, rotate the tires, etc., the lug nuts have to be in good shape so a wrench will grip them tightly.
Because lug nuts are on your wheels, they are exposed to all the elements of the road (salt, water, grime) and really take a beating. Unfortunately, some manufacturers have made them out of two different metals. Underneath is the working part of the lug nut, made of steel. On top is the decorative (the "good looking") part, made out of chrome, stainless steel or aluminum. After a while, the steel part begins to corrode and expands. That changes the shape of the outer cap, sometimes rounding off the hexagonal edges and making it hard (if not impossible) to either loosen or tighten the lug nuts since the wrench won't fit any more.
The reason that's so important is those lug nuts must be functional, especially if you find you have a flat tire somewhere on the road. If the wheel can't come off to be swapped with a spare, it leaves few options, one of which is your vehicle may have to be towed. All that for corroded lug nuts!
When you take your vehicle in for service, the technician who works on it keeps an eye on many things, especially if he or she is removing wheels. It's not unusual for your service advisor to recommend you replace several lug nuts at once since some corrode at a different rate than others. Your repair facility is trying to help you avoid driving a vehicle that has wheels that can't easily be taken off when they need to be.
The good news is there are one-piece lug nuts that don't have the problem the two-piece lug nuts have, so replacing them could eliminate that from happening again any time soon. And that's not "nuts" at all.
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