Understanding Wheel Fasteners

Most people give attention to wheel fasteners only when they get a flat tyre and they need to swap the wheels. Fasteners are very small components that are responsible for holding the wheels onto the vehicle. But, they are also one of the least appreciated items. Although devoting a whole article on wheel fasteners may seem to be a bit overkill but, once you understand its complexities then you will start to appreciate it. We will discuss how the thread size, thread length, seat style, drive style, etc., affect the wheel fitment and also inform you about the proper fastener tightening procedure.

1) Thread Size-

The nuts and bolt should have the same thread size for them to fit like a glove into one another. Usually the nut is marked with the diameter and pitch number. For example, if the nut is marked in inch format as 1/2 x 20 x 1, then 1/2 indicates the diameter of the stud that it will fit into, '20' indicates the pitch of the thread, which is basically number of threads-per-inch of length. Marking '1' means that the nut can accommodate 1 inch of bolt length. Higher pitch value of the nut means that the threads are closely placed and the nut has finer threads.

2) Thread length-

It is important to know about the thread length as it makes sure of the proper fastner engagement. It basically tells us how far the nut travels over the bolt. It is important to ensure that the minimum thread length engagement is equal to the diameter of fastener thread. For example, if the bolt diameter is 1/2 inch, then the nut must cover 1/2 inch length. Vehicle manufacturers generally keep extra thread length for added safety and also for ease of installation.

3) Seat Style-

Proper nut seat style makes sure that the nut presses the wheel onto the hub and everything fits snugly. The 'seat' refers to the end of the nut that makes contact with the fastener pocket. There are generally 3 types of seat styles- Conical, Radius and flat seat type.

Conical fasteners, also called tapered type, features a straight tapered seat area. Usually a 60 degree angle taper is used in these fasteners.

Radius seat, also called 'ball' seat, features a radiused 'ball' shape that settles into the pocket provided on the wheels. They evenly distribute the clamping force and prevent alloy fracture in case of overtighting. Mostly European vehicles use this type of fasteners.

Flat seat fasteners are mostly called mag style fasteners. It got the name mag style because in early days of American performance scene, race wheels were made out of cast magnesium and it was cheaper and easier to get a round hole in a flat hub.

4) Drive Style-

The head of the bolt has a specific type of design that can be used with similar type of socket for locking and unlocking purpose. A hex type head is used most commonly for this purpose. However, different styles like female hex drive and spline drive head (requires dedicated female spline socket) are also used by some manufacturers.

[caption id="attachment_1166" align="alignnone" width="300"] Spline bolt with specific socket[/caption]

[caption id="attachment_1163" align="alignnone" width="300"] Normal hex bolt[/caption]

5) Fastener installation-

It is always better to avoid using impact gun when removing fasteners from alloy wheels because impact gun socket often scratches the fastener pockets. If you have no other option and have to use impact gun, use it at a slow speed setting. Moreover, wheels require a specific window of clamping force, using impact gun often overtightens the nut and this can lead to fracture in the alloy pocket.

It is recommended to use a torque wrench to tighten the fasteners and select the torque setting after referring to owners manual.

[caption id="attachment_1168" align="alignnone" width="300"] Use torque wrench for locking or unlocking fasteners[/caption]

So, keep the above points in mind while purchasing new fasteners for your car, and choose fasteners that match the specifications of the rim.