A liquid or gel that stays fluid in air but cures into a hard plastic when confined between metal threads without oxygen. Strength follows a common color code: purple low strength for small screws, blue medium strength removable with hand tools, red high strength that needs heat of about 250 C to release, and green wicking grade that seeps into already assembled threads. Inactive surfaces such as stainless and zinc plating cure slowly unless a primer is used.
Blue threadlocker on the caliper bracket bolts, red stays on the shelf unless you want to bring the torch next time.
Also heard as
- Loctite
- blue
- red
- thread locking compound
Related terms
Self-loosening
A tightened nut or bolt turning loose by itself, usually because sideways slip in the joint lets it walk off.
Anti-seize
A grease loaded with metal or ceramic particles that stops threads from galling, rusting or bonding under heat.
Nut factor
The empirical constant K in T = KDF that lumps all the friction and geometry between torque and tension.
Breakaway torque
The torque needed to start a tightened fastener turning again, used to audit joints and rate locking features.