Products I know
Threadlockers: choosing the right grade, and getting it approved.
A threadlocker is an anaerobic adhesive that fills the gaps between bolt and nut threads and cures into a solid plastic, so the fastener cannot work loose under vibration. Choosing one comes down to two questions: how strong the lock must be, and whether the part will need to be taken apart later.
How threadlockers work
Threadlockers are anaerobic: they stay liquid in the bottle, where there is air, and cure once they are trapped between metal threads, away from air and in contact with metal. The cured adhesive locks the threads, seals them against moisture and corrosion, and stops the slow loosening that vibration causes.
They replace or support mechanical locking methods such as spring washers, nylon-insert nuts and lock wire, usually at lower cost per joint.
Choosing the grade
| Grade | Typical use | Removal |
|---|---|---|
| Low strength (often purple) | Small screws, adjustment screws, parts opened often | Easy with normal hand tools |
| Medium strength (often blue) | General-purpose choice for most nuts and bolts in machinery | Hand tools |
| High strength (often red) | Studs and permanent assemblies that should not be opened | Usually needs local heat |
| Wicking grade (often green) | Already-assembled fasteners and set screws, applied after assembly | Depends on the grade |
Colours follow a common industry convention, but they vary by brand. Always check the data sheet, especially for temperature limits and the fastener sizes each grade is meant for.
Where threadlocker trials go wrong
- Oily fasteners. Parts straight from the supplier carry oil that slows or weakens the cure. Cleaning, or an oil-tolerant grade, fixes it.
- Inactive surfaces. Stainless steel, zinc-plated and some coated fasteners cure slowly. An activator or the right grade solves it.
- Wrong strength for maintenance. A high-strength grade on a part the maintenance team opens every month creates enemies on the shop floor.
- Torque settings. A threadlocker changes the friction in the thread, so tightening torques may need to be checked against the bolt tension the design needs.
- Dispensing on the line. On high-volume lines, the dispenser and the bead size matter as much as the product.
How I help
For manufacturers and dealers, I take threadlockers into the plants that use the most fasteners: automotive assembly, engineering workshops, pumps and motors, and maintenance departments. For plants, I help narrow down the grade and run a trial with clear success criteria.
Not sure whether you need a threadlocker or a retaining compound? Read threadlocker vs retaining compound.
Questions people ask
Which threadlocker strength should I use?
Medium strength suits most general machinery fasteners and can be removed with hand tools. Use low strength for small or frequently adjusted screws, and high strength only for permanent assemblies that should not be opened. Always check the data sheet for size and temperature limits.
How do you remove a high-strength threadlocker?
Usually by heating the fastener locally to soften the cured adhesive, then removing it with hand tools while it is still hot. The data sheet gives the temperature needed.
Do threadlockers work on stainless steel and plated bolts?
They work, but cure more slowly on these inactive surfaces. An activator or a grade made for inactive metals gives a reliable cure.