Wheel studs are the threaded fastener

Threaded fastener

A threaded fastener is a discrete piece of hardware that has internal or external screw threads. They are usually used for the assembly of multiple parts and facilitate disassembly.The most common types are the screw and nut...

s that hold on the wheel

Wheel

A wheel is a device that allows heavy objects to be moved easily through rotating on an axle through its center, facilitating movement or transportation while supporting a load, or performing labor in machines. Common examples found in transport applications. A wheel, together with an axle,...

s of many automobile

Automobile

An automobile, autocar, motor car or car is a wheeled motor vehicle used for transporting passengers, which also carries its own engine or motor...

s. They are semi-permanently mounted directly to the vehicle hub, usually through the brake drum or brake disk. Lug nut

Lug nut

A lug nut is a fastener, specifically a nut, used to secure a wheel on a vehicle. Typically, lug nuts are found on automobiles, trucks , and other large vehicles utilizing rubber tires.-Design:...

s are fastened over to the wheel stud to secure the wheel. When a wheel is removed for tire changes etc., the stud remains in the hub.

Many automobiles instead use bolts to do this, where removable bolts screw into the wheel hub.

Wheel studs can be either factory equipment or aftermarket

Aftermarket (automotive)

The automotive aftermarket is the secondary market of the automotive industry, concerned with the manufacturing, remanufacturing, distribution, retailing, and installation of all vehicle parts, chemicals, tools, equipment and accessories for light and heavy vehicles, after the sale of the...

 add-ons.

Benefits of studs vs. bolts

The primary advantage of wheel studs over wheel bolts is greater strength due to an increase in clamping force and resistance to loosening.

Another benefit is greater ease for tire changes by creating the ability to lift both the wheel and tire onto the studs creating the ability to hold and locate the assembly during tire changes rather than trying to hold up the wheel and tire while lining up the holes to insert a bolt. Many wheels that use bolts also have one or more small locator pins to assist this: the wheel is lifted onto the pins, then the bolts inserted. Once the bolts are tightened and the wheels fully installed, the pins have no further function whilst the vehicle is being driven.

Types

Wheel studs are replaceable and come in two basic kinds: press-in and screw-in. Welded-in studs are possible but unlikely to be encountered.

Screw-in

Screw-in studs simply screw into the existing threaded

Screw thread

A screw thread, often shortened to thread, is a helical structure used to convert between rotational and linear movement or force. A screw thread is a ridge wrapped around a cylinder or cone in the form of a helix, with the former being called a straight thread and the latter called a tapered thread...

 bolt hole in the hub. The end that screws into the hub is usually either threaded with a higher tolerance fit or installed with a chemical thread-locking fluid

Thread-locking fluid

Thread-locking fluid is a thin, single-component adhesive, applied to the threads of fasteners such as screws and bolts to prevent loosening, leakage, and corrosion. Typically, thread-locking fluids are methacrylate-based, and cure anaerobically...

 to keep it from backing out from the hub when the lug nut is removed.

Press-in

Press-in studs are installed from the back side of the disk or drum hub and may require removal of the hub from the vehicle for installation or removal. They consist of a threaded portion and a larger diameter section that is splined to prevent rotation. The diameter of the splined section is larger than the hole in the hub requiring a press fit to seat the stud. The stud is prevented from being pulled through the hub by a larger diameter stop on the end.

Most press-in studs are designed and recommended to be installed with a mechanical or hydraulic press

Hydraulic press

A hydraulic is a machine using a hydraulic cylinder to generate a compressive force. It uses the hydraulic equivalenta mechanical lever, and was also known as a Bramah press after the inventor, Joseph Bramah, of England. He invented and was issued a patent on this press in 1795...

 to ensure proper seating without damage. It is possible, though not advised, to install a press-in by using a washer

Washer (hardware)

A washer is a thin plate with a hole that is normally used to distribute the load of a threaded fastener, such as a screw or nut. Other uses are as a spacer, spring , wear pad, preload indicating device, locking device, and to reduce vibration...

 and nut

Nut (hardware)

A nut is a type of hardware fastener with a threaded hole. Nuts are almost always used opposite a mating bolt to fasten a stack of parts together. The two partners are kept together by a combination of their threads' friction, a slight stretch of the bolt, and compression of the parts...

to "draw" it into the hub. In doing so, the installer must ensure that the stud is fully seated and that no damage is done to the threaded portion of the stud.

Aftermarket wheel studs

Aftermarket wheel studs offer the ability to mount a wheel that is not factory supplied to that vehicle. Screw-in studs with a larger than original threaded diameter portion permit mounting of wheels with larger diameter holes. Wheel studs of longer length allow the use of wheel spacers to move a wheel further out to compensate for rubbing or backspacing issues or to make the wheel look like it is larger than factory standard.