used when you want to make sure screws stay tight. With RC cars threadlocker is used in the parts of the car that are subject to vibration
and spinning. Most commonly threadlocker is used on off-road RC
cars where the components are subject to vibration and greater
impact forces than touring cars and it is only used on metal
surfaces, never on plastic.
Usually threadlocker is liquid so it is important to keep it away from surfaces where it can hinder the movements of moving parts. Typically, it is used on the motor mounts that are mounted at the bottom of the car and when mounting the steering blocks to C-hubs.
Threadlocker is available in several different types in terms of strength, but in an RC hobby the medium strength threadlocker (the blue one) is strong enough for all purposes. Generally, all RC equipment manufacturers sell the blue compound.
Here are the different types of threadlocker:
Low strength: purple
High temperature: red
Using threadlocker is easy. Depending on the case, you apply the liquid on the thread of the screw (clean the thread first from oil etc.) or nut, depending on its location. Half a drop is enough on the thread of the screw and then it can be screwed as tightly as needed. Threadlocker dries within a couple of minutes.