Thread lock and locking nuts

In some cases, a bolt should be fitted with a small amount of thread lock applied to help reduce the risk of it slackening. This is essentially a mild glue, and manufacturers such as Loctite produce thread lock in a bottle and tube. Avoid saturating the thread in thread lock because a small amount is usually sufficient.

Some bolts are supplied with thread lock already applied, so they may need to be replaced if removed because the thread lock won’t be as effective when fitting the bolt for a second time. Such bolts are often used for suspension and brake components. In some cases, it may be possible to clean the thread and apply thread lock to re-use the bolt.

Nylon insert nuts have a small amount of nylon above the thread to help provide resistance and reduce the risk of the fastening loosening. They are usually referred to as nyloc nuts. After undoing such a nut, the nylon insert isn’t as effective and so it’s recommended to renew the nut, although re-using it in a non- critical area of the car is feasible if it still remains effective (meaning it cannot be turned with your fingers). The nylon can melt with heat, which helps with undoing an old stubborn fastening, but also means they should not be used on or near hot components such as an exhaust system. Where a locking nut is needed for a hot component and a nylon locking nut isn’t recommended, an all-steel self-locking nut can be used instead. These can be re-used up to six times.

Doubling-up on nuts is another means of locking a fastening because the two nuts are tightened against each other and this makes them very difficult to turn as a unit. Half nuts are often used in this situation because they take up less room since they are shorter in height.

These are two types of all-metal locking nuts for use where nylon might melt. The deformed ends on each of them provide the grip.

Two nuts can also be wound against each other to provide a lock. Often a half nut (ie half the thickness) is used for this.

When fitting a nyloc nut, the thread on the bolt should protrude by two full turns to be properly secured. This one is not there yet!

A light dab of thread lock is usually sufficient to keep fastenings secure, but they must be grease-free when it is used.

Nyloc nuts have a nylon insert to resist loosening. Blue nylon means it is metric, while white means it is unified or imperial.