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What Are Lug Nuts?

It’s easy to lose track of the bits and pieces that go into your vehicle – what they do, how to keep them maintained, what to watch out for and so on. Lug nuts sometimes slip beneath notice for drivers focusing on more central components. Understanding lug nuts is simple, though, and well worth keeping in mind to prevent issues with your wheels down the road.

What Are Lug Nuts?

A lug nut is a type of fastener where one end (the seat) is rounded or tapered, though the exact shape varies. Lug nuts fasten a wheel’s hub to threaded wheel studs on the vehicle’s axle, securing the wheel in place and centering it properly on the axle. The lug is placed onto the wheel stud atop the wheel, with the lug’s seat in contact with the hub.

Typically, lug nuts are made of chrome-plated steel – the chromium granting corrosion resistance – but titanium or anodized aluminum lug nuts exist for those who want lighter-weight parts, typically for racing cars. For most folks, chrome steel will do.

The particular size and model of lug nuts needed depends on the car model and the axle it uses. The correct lug nut seat depends on the wheel itself. Conical/tapered lug nuts are most common, but ball/radius and flat-seat lugs are also in common use. While aftermarket wheels are often designed to match OEM lugs for a vehicle, some require a new set to make a proper fit. Stripped or damaged lug nuts can make removing a wheel very difficult and should be replaced when needed. Many newer vehicles are equipped with a locking lug nut that requires a wheel lock tool to be used when removing lug nuts. In some cases, there may be one locking lug per wheel. The wheel lock key should be kept in a convenient place in your vehicle such as in the glove box or with other spare tire tools.

Installing and Tightening Lug Nuts

Certified auto technicians are ready and able to replace worn or damaged lug nuts, on their own or as part of tire maintenance, but it helps to understand the process if you need to do it yourself, so you can avoid damaging the threads or over-tightening the lug to the point where it can’t be removed again.

The main tools you’ll need are a socket wrench and a torque wrench. Some mechanics use impact wrenches – a power tool equivalent of a wrench – for speed and minimal effort, but inexperienced users could overdo it and damage the lug or wheel studs. You also should have a workshop manual on hand to consult for setting the torque wrench properly.

The nut should initially be placed by hand then tightened partially with a socket wrench, just enough to fit snug with the wheel. Following this, a properly calibrated torque wrench tightens each nut fully until the wrench clicks. A star or crisscross pattern is ideal to ensure evenly distributed stress. Lubricant is generally not needed, as the torque wrench will be able to handle the task if set properly. A steady hand and proper specifications will have your lug nuts installed or tightened in no time.

Correctly applying torque is critical to the proper installation of lugs without causing any damage. Torque wrenches can be calibrated to a fixed tightness measured by foot per pound, and the manual will tell you the right torque to use. For most modern vehicles, this is somewhere within 60 to 120 ft./lbs. Impact wrenches deliver intense torque far higher than vehicle specifications: up to 450 ft./lbs., without any easy way to mitigate or control it.

What About Lug Bolts?

The term “lug bolts” comes up sometimes in discussing tire and wheel maintenance and may get confused with lug nuts or assumed to be a synonym. In truth, the two, while serving similar functions in fastening a wheel in place, are designed and used differently.

A lug bolt, as the name suggests, features a threaded length of a bolt extending from the lug’s seat. Though the exterior ‘cap’ looks much like a lug nut, this threading changes how a lug bolt is used. Vehicles designed for lug bolts lack wheel studs on the axle’s hub, as the lug bolt serves this purpose; the bolt is threaded through the wheel hub and into the axle. There are separate engineering considerations for each type of fastener, but most cars and wheels are designed mainly or solely for one or the other, so it is vital to understand that before purchasing parts or attempting installation.

Stud bolts, which are bolts with two threaded ends and no head, also exist for use as fasteners. Functionally, this acts as a wheel stud that is installed on its own then capped with a lug nut.