Threadlockers are anaerobic products used to secure threaded metal fasteners against self-loosening caused by vibration, shock, cyclic loading and temperature changes. A correctly selected product fills the microscopic clearance between mating threads, limits micro-movement and can also help seal the joint and protect the thread gap from corrosion.
The key to a reliable result is not simply choosing a colour or the “strongest” grade. Selection should be based on required strength, thread size, substrate, operating temperature, serviceability and the actual assembly process. The exact application and curing procedure should always be confirmed in the current TDS for the selected product.
Key takeaways
- Anaerobic threadlockers are usually one-component products designed primarily for metal threaded joints.
- They cure after air is excluded from the joint gap and the product is confined between metal surfaces.
- Do not select a threadlocker by colour alone: check strength, viscosity, thread size, substrate, temperature and planned disassembly.
- Medium-strength products are usually preferred for serviceable joints; high-strength grades require a defined disassembly procedure.
- Fixture time is not the same as full cure. The exact time before loading must come from the current TDS.
- A threadlocker and a pipe thread sealant may both use anaerobic chemistry, but they are designed for different primary tasks.
What are anaerobic threadlockers and how do they work?
Anaerobic threadlockers remain liquid while exposed to air. Once the product is confined between mating metal threads, oxygen availability is greatly reduced and the curing reaction can proceed. The metal surface participates in the initiation of the cure.
After curing, the material fills the free space between the threads. This limits micro-movement and helps stabilise the joint against vibration and shock. In many applications it also reduces the path through which moisture or process fluids can enter the threaded gap.
Video: anaerobic adhesives – applications and selection
This original Melkib playlist is retained from the previous version of the article. It includes practical materials on threadlocking, sealing and typical selection or application mistakes.
Why do threaded joints loosen?
A threaded joint works correctly when it maintains the required preload. Transverse vibration, shock, cyclic loading and micro-slip can reduce clamping force and allow the fastener to rotate relative to the mating part.
An anaerobic threadlocker fills the clearance between the threads and, after cure, reduces relative movement. This is why it is commonly used in pumps, gearboxes, electric motors, presses, production machinery and maintenance assemblies exposed to vibration.
How to select a threadlocker
1. Decide whether the joint must be serviceable
For joints that will be dismantled during normal maintenance, a medium-strength threadlocker is usually the more practical choice. High-strength products are selected where resistance to loosening is the priority and disassembly is expected to be infrequent or carried out using a defined service procedure.
2. Check the thread size
Different threadlockers are formulated for different thread sizes and clearances. Very small adjusting screws, standard machine fasteners and large studs may require different viscosity and strength levels.
3. Identify the substrate
Anaerobic products are intended mainly for metal-to-metal assemblies. The cure rate can depend on the substrate and the specific formulation. Older anaerobic systems often cure faster on so-called active metals and more slowly on passive surfaces such as stainless steel, aluminium or plated parts.
Modern primerless grades can reduce this limitation. For example, Henkel describes LOCTITE 243 and LOCTITE 270 as products that work on passive metals without a separate primer. This is why activator use should be based on the TDS of the specific product, not on a universal rule that every stainless-steel thread requires activation.
4. Check operating temperature and environment
Temperature influences both curing and long-term performance. Chemical exposure, vibration and thermal cycling can also affect the joint. Use the product-specific TDS rather than relying on a generic temperature range for “anaerobic adhesives”.
5. Plan disassembly before choosing high strength
High-strength grades can make future service more difficult. Henkel specifies a heat-assisted disassembly procedure for LOCTITE 270. The required temperature and method must be checked in the current TDS and assessed against nearby seals, coatings, plastics and heat-sensitive components.
How to apply threadlocker step by step
- Check the application. Confirm that the joint is metallic and that the chosen product matches the thread size, required strength, temperature and service plan.
- Clean the thread. Remove dirt, loose corrosion products and heavy oil or grease. Even where a modern product tolerates light oil contamination, a controlled clean surface gives a more repeatable assembly process.
- Allow the cleaner to evaporate. If a solvent-based cleaner is used, do not trap wet cleaner inside the joint.
- Apply the threadlocker in the working area. Use enough product to wet the relevant threads without uncontrolled over-application.
- For blind holes, apply product inside the hole as well. Otherwise the male thread can push the adhesive out of the active zone during assembly.
- Assemble and tighten correctly. Tighten the fastener to the specified assembly torque or process requirement.
- Do not disturb the joint during early cure. Movement can damage the developing polymer network.
- Wait for the required cure before loading. Fixture time and full cure are different values. Use the current TDS to define when the assembly can be handled and when it can be put into full service.
How long does threadlocker take to cure?
There is no single curing time for all anaerobic threadlockers. Cure depends on:
- the exact product,
- substrate material and surface condition,
- temperature,
- thread clearance,
- use of an activator where specified,
- contamination and surface preparation.
Many anaerobic products reach handling or fixture strength much earlier than full cure. Do not use “it feels locked” as the criterion for commissioning a critical joint.
Medium strength or high strength?
| Selection factor | Medium strength | High strength |
|---|---|---|
| Typical objective | Prevent loosening while retaining normal serviceability. | Maximise resistance to loosening where disassembly is not a routine operation. |
| Typical example | LOCTITE 243. | LOCTITE 270. |
| Disassembly | Typically removable with ordinary hand tools when used within the product specification. | May require local heating or another TDS-defined service procedure. |
| Typical maintenance use | Pumps, gearboxes, machine covers, standard bolted assemblies requiring future maintenance. | Studs, heavily loaded fasteners and assemblies intended to remain locked for long periods. |
Do not choose threadlocker by colour alone
Colour is useful for quick identification within a specific product range, but it is not a universal engineering standard. A blue product is often medium strength and a green product may be high strength or penetrating, but the exact function must always be confirmed from the product name and TDS.
For example, LOCTITE 243 is a blue medium-strength threadlocker, while LOCTITE 270 is a green high-strength threadlocker. Other green anaerobic products may be designed for completely different tasks.
Threadlocker vs pipe thread sealant
Threadlocking and pipe-thread sealing are related but different applications.
- Threadlocker: the primary objective is to prevent a fastener from self-loosening under vibration or dynamic loading.
- Thread sealant: the primary objective is to seal a threaded pipe or fitting against leakage.
LOCTITE 577 is an example of a one-component anaerobic thread sealant designed for threaded metal pipes and fittings. It fills the space between threaded parts and provides sealing while also locking the connection. It should not be treated as a direct substitute for a conventional bolt threadlocker merely because both products cure anaerobically.
Products used in the current Melkib process guide
| Product | Role in the process |
|---|---|
| LOCTITE SF 7063 – ID 3526 | Cleaner and degreaser used for surface preparation before bonding or sealing. |
| LOCTITE 243 – ID 3541 | Medium-strength threadlocker for serviceable metal threaded joints; Henkel states that it can normally be removed with hand tools. |
| LOCTITE 270 – ID 3544 | High-strength threadlocker for assemblies where maximum resistance to loosening is the priority. |
| LOCTITE 577 – ID 1844 | Anaerobic thread sealant for metal pipes and fittings where sealing is the primary requirement. |
...
Common threadlocking mistakes
- Choosing only by colour. Check the actual strength, viscosity, thread range, temperature and disassembly requirements.
- Applying to a dirty thread without process control. Oil-tolerant does not mean that uncontrolled contamination is good practice.
- Using too little product. Incomplete coverage can leave part of the thread unsupported.
- Flooding the joint. Excessive dosing adds mess and cost without improving a correctly filled joint.
- Applying only to the male thread in a deep blind hole. The adhesive may be displaced outside the working zone during assembly.
- Moving the joint during cure. This can disturb the developing bond.
- Loading too early. Fixture time is not full cure.
- Using high strength without a service plan. Disassembly must be considered before assembly, not after the machine fails.
When should a threadlocker be used?
Threadlockers are particularly useful where a threaded assembly is exposed to vibration, shock, cyclic loading, risk of leakage or corrosion within the thread gap. Typical examples include:
- pumps and gearboxes,
- electric motors and drives,
- presses and production machinery,
- fans and rotating equipment,
- maintenance and repair assemblies,
- metal fasteners that must retain preload under vibration.
For a broader discussion of how substrate activity and process conditions affect cure, see Anaerobic adhesives and the type of material.
FAQ: anaerobic threadlockers
How do you apply threadlocker?
Clean the thread, select a product with the required strength, apply it in the working area, assemble to the specified torque and allow the joint to cure. For blind holes, apply product inside the hole as well as to the male thread.
Does threadlocker cure because there is no oxygen?
Oxygen exclusion is a key part of the mechanism, but the chemistry is designed to cure while confined between suitable metal surfaces. Product formulation, metal type, temperature and gap all influence cure behaviour.
Is an activator always required on stainless steel?
No. Some older or product-specific anaerobic systems cure more slowly on passive metals, but modern primerless products such as LOCTITE 243 and LOCTITE 270 are specified by Henkel for passive substrates without a separate primer. Follow the TDS for the exact product.
Which threadlocker should be used for serviceable joints?
A medium-strength grade is commonly selected when future disassembly with hand tools is expected. LOCTITE 243 is a typical example.
Is green threadlocker always high strength?
No. Colour is not a universal technical specification. LOCTITE 270 is a green high-strength threadlocker, but other green anaerobic products can have different functions.
Can threadlocker replace a spring washer?
It works by a different mechanism. A cured anaerobic threadlocker fills the clearance between the threads and limits micro-movement. Whether it replaces a mechanical locking element must be decided from the joint design, loads, service requirements and assembly SOP.
Is LOCTITE 577 a threadlocker?
It is primarily a thread sealant for metal pipes and fittings. It uses anaerobic cure and also locks the threaded connection, but the design objective is sealing rather than securing a conventional bolt against vibration.
Need to choose a threadlocker for a real assembly?
Start with the thread size, substrate, operating temperature, vibration level and planned disassembly. These details make it much easier to select the correct strength and application process.
Log in with Facebook
Log in with Google