Threadlockers and retaining compounds are both anaerobic adhesives, and they share a curing mechanism, but they are formulated for different jobs. Knowing which one a joint needs is the first step toward a reliable, cost-effective assembly.
A Shared Curing Principle
Both products stay liquid in air and cure rapidly only when confined between close-fitting metal surfaces without oxygen, with metal ions acting as the catalyst. That is why both are effective at preventing loosening, sealing against leaks, and resisting corrosion in confined metal-to-metal joints. Their formulations and intended applications diverge from there.
Threadlockers: Securing Threaded Fasteners
Threadlockers are anaerobic adhesives for threaded assemblies, meaning nuts, bolts, screws, and studs. Their job is to keep fasteners from loosening under vibration, thermal cycling, or shock.
Applied to the threads, the liquid flows into the microscopic gaps between mating threads. Once assembled, the exclusion of air triggers the cure, forming a solid bond that locks the threads, removes radial play, and holds clamp load.
Key points:
- Target: threaded fasteners.
- Gap: the small, consistent clearance of a thread fit, typically up to about 0.15 mm.
- Viscosity: low to medium, to flow into fine threads.
- Strength grades: low strength for small fasteners needing frequent removal; medium strength as the general-purpose choice, removable with hand tools; high strength for permanent joints that come apart only with heat and force; wicking grade with very low viscosity to penetrate pre-assembled fasteners.
- Benefits: resists vibrational loosening, seals threads against leaks and corrosion, and can replace lock washers and cotter pins, simplifying inventory.
Retaining Compounds: Strengthening Cylindrical Fits
Retaining compounds are anaerobic adhesives for non-threaded cylindrical assemblies: bearings, bushings, gears, pulleys, and shafts fitted into housings or onto shafts. They augment or replace press and shrink fits by bonding across the entire mating surface.
Applied to the cylindrical surfaces, the compound fills the microscopic voids that remain even in a precise fit. On assembly, air exclusion cures it, turning the fit into a unitized joint with full surface contact.
Key points:
- Target: cylindrical, non-threaded assemblies.
- Gap: larger and more variable than threadlockers, typically up to 0.25 mm, and up to 0.5 mm for some grades.
- Viscosity: generally higher, to bridge larger clearances and resist run-out.
- Strength: higher shear strength than threadlockers, because the bond area is larger and must transmit significant loads.
- Benefits: increases the strength of press and slip fits, eliminates fretting corrosion from micro-movement, seals against contaminants, and allows looser machining tolerances, which can reduce cost.
Choosing between the two is usually clear once you identify whether you are securing a bolt or strengthening a cylindrical joint. Email Us to review your assemblies with Incure’s technical team.
Key Distinctions at a Glance
| Feature | Threadlocker | Retaining Compound |
|---|---|---|
| Primary application | Threaded fasteners | Cylindrical non-threaded parts |
| Function | Prevent loosening, seal threads | Strengthen cylindrical fits, prevent fretting |
| Gap filling | Smaller, consistent, up to about 0.15 mm | Larger, variable, up to about 0.5 mm |
| Strength focus | Breakaway and prevailing torque | Shear strength, axial and radial load |
| Viscosity | Lower to medium | Often higher |
| Disassembly | Easy to permanent by grade | Often challenging, some permanent |
Application Notes for Both
Surface preparation and metal type apply equally. Clean threads or bores of oil, grease, and dirt for reliable cure. On passive metals such as stainless steel, aluminum, or plated surfaces, use an activator. Account for temperature, since cure slows in the cold. Choose the strength grade from the fastener or joint size, the required disassembly force, and how critical the joint is.
Common Selection Errors
- Using a threadlocker on a slip fit: a threadlocker’s low viscosity and lower shear strength are wrong for a bearing or bushing. It will not build the shear capacity a retaining compound provides across the cylindrical bond area, and the part can migrate under load.
- Using a retaining compound on threads: the higher viscosity resists flowing into fine thread roots, so coverage is incomplete and prevailing torque is inconsistent.
- Ignoring gap on a worn fit: if a shaft or bore is worn beyond the compound’s rated gap, the bond will not develop full strength. Measure the actual clearance and select a grade rated for it, or restore the fit.
- Defaulting to maximum strength: a high-strength grade on a bearing you may need to replace makes disassembly destructive. Match strength to the maintenance plan.
Using Both on One Assembly
Many machines use both products in different locations. A gearbox might use a retaining compound to seat the output bearing in its housing and a medium-strength threadlocker on the cover bolts. There is no conflict, since each cures in its own confined joint. Specify each location separately in the bill of materials, note the grade and any activator, and include removal instructions in the service manual so field technicians apply the right heat and torque for each.
How Incure Supports Assembly
Incure offers anaerobic threadlockers and retaining compounds across strength and viscosity ranges, with technical support on matching the product to joint type, materials, operating conditions, and disassembly needs, plus guidance on surface preparation, dispensing, and cure.
For related guidance, see how thermal expansion mismatch loads a bonded joint, our comparison of adhesive strength for heavy-duty repairs, and how cure speed varies across chemistries.
Summary
Threadlockers secure threaded fasteners against loosening; retaining compounds strengthen cylindrical fits and stop fretting. They share a cure mechanism but not an application. Identify the joint type, select the strength grade for the load and service plan, and prepare surfaces properly.
Contact Our Team to match an anaerobic adhesive to your assembly.
Visit www.incurelab.com for more information.