Thread lock should only be used on metal-to-metal connections, never on plastic parts. The thread lock turns into a plastic-like substance itself that can damage plastic parts if you try to unfasten them. Areas of an RC that can benefit from the use of thread lock includes metal throttle linkages, aluminum bulkheads, and metal steering linkages. Thread lock is not for internal engine parts.
Although thread lock gives screws more holding power, you can still loosen and remove them for maintenance by applying a little added pressure. Blue thread locking compounds are typically used on RCs. Stronger red and green thread locking compounds require heat to remove. You can purchase thread lock at your local hobby shop or an auto parts store.
Sometimes referred to generically (and erroneously) as Loctite, Loctite Threadlockers is a specific brand of thread lock adhesive from a company named Henkel.

