Locking wheel nuts are special nuts that are inserted through your wheels which secure them to the vehicle. To undo the nuts you need the corresponding locking nut, and without it, it is very difficult to take them off. Cars are fitted with these to stop the wheels being stolen as previous to locking wheel nuts, people used to come out to the their car in the morning to find that all four wheels had been taken and the car was left on bricks. This was especially true for cars with expensive alloy wheels that could then be sold on.

If you take your car to a garage to have new tyres, wheels of any part that requires the wheels to be removed, the garage will need this nut to remove them. If you do not have it you may find you have issues getting the repair work completed. Some garages have a universal one, although in my experience there are very few and far between that do.

Always keep it is a safe place ideally in the boot or glove box of the car.