Threads on wheel studs, wheel hubs, wheel bolts and wheel nuts

In today’s blog article we want to take a little excursion to the car repair shop. To fix the wheel to the car, screw connections are used. These screw connections can differ from country to country. In Asia and America it is more common that vehicles have wheel nuts. In Europe, the wheels are fixed to the hub with wheel bolts – also called wheel screws.

What are wheel bolts and wheel screws?

Wheel studs are therefore special bolts on which an external thread is cut and with which the wheel is fixed to the vehicle.

What are wheel hubs?

The wheel hub is the connecting element that connects wheels with the axle or drive shaft. The wheel hub has holes with an internal thread. The wheel bolts are screwed into this threaded hole.

Thread types for wheel studs and wheel hubs

As with almost all threads used in the automotive industry, the thread type for wheel studs and wheel hubs is a metric fine thread (MF or also M) with a flank angle of 60 degrees. For the American region, the inch equivalent of the metric fine thread is the American fine thread Unified National Fine Thread (UNF). The UNF also has a flank angle of 60 degrees.

More information about the thread types is available in this article: The 13 most important thread types you should know

If the metric fine thread is simply abbreviated with M, the fine thread can only be unmasked by the standard thread based on the pitch.

Here is an overview of the nominal size, the pitch and the core hole diameter: Core hole dimensions – The tables

Thread sizes for wheel studs and wheel hubs

Here we list an overview of the most common thread sizes for wheel studs and wheel hubs:

MF 12 x 1,25 (nominal dimension 12 / 1,25 mm pitch)
MF 12 x 1,5 (nominal dimension 12 / 1,5 mm pitch)
MF 14 x 1,25 (nominal dimension 14 / 1,25 mm pitch/ for BMW)
MF 14 x 1,5 (nominal dimension 14 / 1,5 mm pitch)
UNF ½“ – 20 ( nominal dimension ½“ / 20 threads per inch / 12,7 mm Thread diameter)

The bolt length can vary greatly according to the make of car. A clear list of the assignment of wheel bolts and nuts by vehicle type can be found here..

Dirty or corroded threads on wheel bolts and wheel hubs

Due to the high stress, the threads may corrode or rust and become dirty. Then it is necessary to re-cut the thread or even cut a completely new thread. The defective thread can be regained a perfect grip with the appropriate tap and can be screwed in as soft as butter.

Cutting tap or hand tap set?

You can work with a cutting tap as well as with a set. For re-cutting, a cutting tap is usually sufficient. The lead-in is very short with the cutting tap, so that the tap cuts directly without the existing drill hole serving as a guide orientation.

In a set, on the other hand, the thread is cut much more carefully. It is therefore particularly suitable for clean, sensitive and careful work. If you want to cut a completely new thread, we recommend a set of hand taps. For fine threads, the set consists of two hand taps (taper tap and finishing tap).

How do I cut a thread on wheel studs or wheel hubs?

The thread on wheel studs and wheel hubs is cut or recut like all other threads. The tap is used for the internal thread. Dies or cutting nuts for the external thread on the bolt.

You should note the following:

1. each time you cut a thread, you should use thread paste or cutting oil.

2. put the tap in place, make one turn and then half a turn back again.

3. clean the wheel hub or bolt from chips and lubricants after the thread has been cut.

If the thread of the wheel hub is too badly damaged, e.g. because a torque impact wrench has been used and the screw has been set at an angle by mistake, all that remains is to drill out the thread and cut a larger one. Alternatively, you can have the entire wheel hub replaced.

If the thread of the wheel bolts is broken, a die for external threads is used.

What can you do with a destroyed wheel bolt head?

You have several possibilities when the wheel bolt head is destroyed to unscrew the thread.

Method 1: Screw extractor set or wheel bolt repair set

If the head is destroyed and they cannot use the key, they can resort to more radical means.

1. drill the bolt head with a twist drill for stainless steel (HSS) and a cordless screwdriver.

2. then use a screw extractor set. Screw extractors are also called left-handed extractors.

A video tutorial and detailed instructions for use of the screw extractor set can be found here on our blog:

Method 2: Rim lock disassembly kit

If the rim lock key has been lost, you can buy the matching key from your trusted dealer. Another possibility is to use a professional rim lock cracker set.