By Dr. Jody Muelaner
Threadlocker, also known as thread-locking fluid, is an adhesive used to prevent threaded fasteners from loosening. It may also be used to seal threads and prevent corrosion.
Typically referred to as its original brand name Loctite, threadlocker is supplied as a thin fluid in a bottle. The adhesive easily drips onto the threads of fasteners (such as bolts and screws) from a nozzle-top bottle. The fastener can then be tightened into place. The liquid will cure to form a layer of thermoset plastic between the male and female fastener threads.
A color-coded label typically indicates the different strengths of threadlocker available.
- Low-strength threadlocker prevents fasteners from working loose under vibration while providing fairly simple disassembly and reassembly. Loctite’s “Purple” is suitable for use on low-strength materials, such as aluminum and brass. It also works on smaller, more delicate fasteners, such as electronic devices.
- Medium-strength threadlocker requires a significant force to break the lock — such as by using a mallet on a spanner. Loctite’s “Blue” is medium-strength. It fully cures in 24 hours and can be dissembled with hand tools. The brand’s “Green” is a wicking threadlocker that can be applied to pre-assembled fasteners, such as electrical connectors and set screws. It provides medium to high-strength adhesion and can be removed with heat and hand tools.
- High-strength threadlocker would require a force that could shear off the head of the fastener. It is strong. Generally, heat is used first to soften the adhesive for simpler removal. Loctite’s “Red” is high-strength, fully cures in 24 hours, and requires heat for disassembly.
Alternative methods of locking threaded fasteners include locknuts, jam nuts, lock washers, and safety wire. In critical applications, these may be used in conjunction with threadlocker.