Anaerobic chemistry cures the same way whether it's sitting between a bearing and a shaft or wicked into a threaded fastener — but that doesn't mean a retaining compound and a threadlocker are interchangeable, and using the wrong one on threads can cost you more than it saves. What Retaining Compounds Are Actually Designed For Retaining compounds are formulated to enhance the strength and integrity of non-threaded, cylindrical metal assemblies — bearings, shafts, gears, and housings — by filling the microscopic gaps and irregularities between mating surfaces. That fill converts a loose or slip fit into a unitized, full-contact assembly, which increases shear and axial load capacity, prevents fretting corrosion, and allows for looser manufacturing tolerances. Why Threads Are a Different Geometry Problem Threaded fasteners have specific, relatively large, and consistent helical gaps designed for mechanical engagement — a fundamentally different geometry than the tight, often irregular clearance a retaining compound is formulated to fill. Applying a retaining compound to threads can interfere with proper seating and engagement, since the product's viscosity and cure characteristics are optimized for the smaller, more uniform gaps found in cylindrical fits, not the helical thread path. There's also a practical risk: the higher viscosity of many retaining compounds makes precise application to threads difficult without excessive squeeze-out, and any uncured excess exposed to air won't cure, leaving a residue that has to be cleaned up. What Happens If You Use the Wrong One Anyway In practice, a retaining compound applied to threads doesn't necessarily fail outright — it may cure and provide some locking effect, which is exactly what makes the mistake hard to catch during initial assembly and inspection. The problems tend to surface later: at disassembly, where the mismatch between the compound's high shear strength and the thread's smaller engagement area makes removal far harder than a properly selected threadlocker would have been, sometimes requiring more heat and force than the fastener or surrounding component can safely tolerate. A threadlocker misapplied to a cylindrical retaining application has the opposite problem — its lower viscosity and strength, tuned for helical thread gaps, may not fill a cylindrical fit's larger annular clearance completely, leaving a weaker bond than the application actually needs. Why Threadlockers Exist as a Separate Product Category Threadlockers are purpose-built for threaded fasteners, formulated with viscosities and strengths specifically tuned to wick into the thread path, resist rotational loosening, and — depending on the strength grade selected — allow disassembly without stripping threads or damaging the fastener. That's a meaningfully different design goal than a retaining compound's job of maximizing shear strength across a cylindrical bond area, and a high-strength retaining compound applied to threads can make disassembly far more difficult than intended, risking stripped threads or a broken fastener. The Practical Distinction Retaining compounds are best suited to radial and axial retention in non-threaded, cylindrical parts. Threadlockers are best suited to rotational prevention and sealing in threaded fasteners. Both are anaerobic technologies and both cure the same way chemically, but…

Press fits, shrink fits, keys, and splines have secured cylindrical components for generations, but each one carries the same limitation: incomplete surface contact that leaves an assembly vulnerable to fretting, backlash, and fatigue under sustained vibration. The Core Function of a Retaining Compound Retaining compounds fill the microscopic gaps and imperfections between mating cylindrical metal surfaces. Once assembled, the absence of air triggers a rapid cure that transforms the liquid into a tough, durable thermoset plastic, producing full surface-to-surface contact rather than the partial contact typical of a mechanical fit. That full contact increases shear and axial strength, prevents fretting corrosion by eliminating micro-movement, maintains concentricity for rotational accuracy, seals against contaminants, and allows for looser machining tolerances than a heavy press fit would require. Bearing Retention Press fits and shrink fits can distort thin-walled housings or bearing races, shortening bearing life and increasing friction. Retaining compounds allow a slip fit instead, eliminating that installation stress while still providing full-contact retention that resists fretting corrosion — a common approach in wheel bearings, motor bearings, pump impellers, and conveyor rollers. Mounting Gears, Pulleys, Sprockets, and Flywheels Keys, splines, and set screws can introduce backlash and uneven load distribution over time, especially under dynamic loads. A retaining compound provides a complete, backlash-free bond that distributes torque uniformly across the contact area, which reduces noise and vibration in gearboxes, industrial mixers, and similar power-transmission assemblies. Securing Bushings and Sleeves Retaining compounds keep bushings fixed against rotation or axial movement in hydraulic cylinder bores and pivot points on heavy equipment, and they're also useful for repairing worn seats where original machining tolerances have degraded over years of service. Fixing Oil Filler Tubes and Threaded Inserts in Castings Non-load-bearing cylindrical components, such as oil filler tubes or threaded inserts pressed into a casting, are another common retaining-compound application even though they don't carry significant mechanical load. Here the priority shifts from strength to a reliable, leak-proof seal that also holds the component in place against the vibration typical of an engine block or pump body. A retaining compound handles both requirements simultaneously — filling the annular gap for a permanent seal while still providing enough mechanical retention to keep the insert from working loose over the equipment's service life. Liner Retention and Rotor-to-Shaft Bonding Cylinder liner retention in internal combustion engines depends on both structural integrity and a reliable seal against coolant or oil leakage — a job retaining compound handles well. The same full-contact principle applies to rotor-to-shaft bonding in electric motors, where concentricity directly affects motor performance and vibration. Fixing Worn Fits Without Re-Machining One of the more underused applications for retaining compound is restoring a fit that has worn loose over years of service rather than machining a new part to tighter tolerance. A bearing bore that has worn slightly oversized, or a shaft seat that no longer holds a tight press fit, can often be brought back to full functional tightness by filling the enlarged clearance with a retaining compound sized…

Calling a retaining compound "permanent" oversimplifies a decision that has real consequences for maintenance planning — the truth is that permanence is a spectrum, and where a given product sits on it depends entirely on the strength grade you select. The Nuance Behind "Permanent" Bonding High-strength retaining compounds create a rigid, durable bond that is genuinely difficult to disassemble, but "difficult" is not the same as "impossible." Whether a retaining-compound joint can be taken apart — and how much effort that takes — comes down to two variables: the specific strength grade used at assembly, and the disassembly method applied afterward. Strength Grade Determines Disassembly Difficulty High-strength compounds are formulated for maximum load transmission and resistance to vibration, shock, and extreme operating conditions. They're intended for assemblies unlikely to need disassembly over the product's service life, and removal typically requires localized heat combined with significant mechanical force. Medium-strength compounds provide substantial bonding strength while still allowing disassembly with standard hand tools or moderate mechanical force — the right choice for components that may need periodic replacement or service. Low-strength formulations exist for applications where frequent, easy disassembly is the priority, even in a tight-tolerance fit. How Disassembly Actually Works Heat is the most common and effective disassembly method for anaerobic bonds, since these compounds are thermoset plastics that soften and lose strength when heated — typically in the range of 250°C to 300°C (482°F to 572°F) for high-strength products. Applying localized heat directly to the bonded joint, then separating the components with a puller or press while the bond is still softened, is standard practice; heating only the joint area avoids damaging adjacent components. For medium-strength compounds, standard mechanical tools alone are often sufficient without any heat application, though attempting the same approach on a high-strength bond risks bending shafts or cracking housings under the force required. Chemical dissolution using solvents is rarely practical for a fully cured bond — it's better suited to cleaning uncured excess or residual film after mechanical separation. Designing for Future Disassembly The decision of which strength grade to use should happen at the design stage, not after a component has already failed and needs replacing. If a part is likely to need periodic service, a medium-strength compound with hand-tool disassembly is the more practical choice; if the assembly is meant to be a permanent fixture for the product's operational life, a high-strength compound is appropriate. Access for heat application should also be considered during design if a high-strength compound is chosen, since disassembly without adequate access becomes significantly harder in the field. What Happens If You Guess Wrong on Strength Grade Specifying too high a strength grade for a component that turns out to need regular servicing creates a real maintenance cost: technicians end up applying more heat and force than a joint's other components can safely tolerate, risking damage to seals, bearings, or housings that were otherwise still serviceable. Specifying too low a strength grade for what turns out to be a permanent,…

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…

A press fit that looks solid on the assembly bench is still only touching itself across a fraction of its mating surface — the rest is microscopic air gaps waiting to become fretting corrosion once the shaft starts turning. What a Retaining Compound Does A retaining compound is an anaerobic adhesive engineered specifically for bonding cylindrical metal parts — bearings, bushings, gears, pulleys, and shafts — into housings or onto shafts. Like other anaerobic chemistries, it cures rapidly in the absence of air once confined between close-fitting metal surfaces. Its job is to fill the microscopic gaps and surface imperfections that exist even in precisely machined parts, converting what would otherwise be a loose or marginal mechanical fit into a rigid, unitized assembly. Why Retaining Compounds Outperform Mechanical Fits Alone Even a well-executed interference press fit typically achieves true metal-to-metal contact across only a fraction of the mating surface — often as little as 30 percent — leaving the rest as air pockets. Those gaps allow micro-movement under vibration and thermal cycling, concentrate load on the limited contact area, and trap air and moisture that promote corrosion. A retaining compound eliminates all three problems at once: it fills every void, cures into a continuous bond across the full mating surface, distributes load evenly rather than concentrating it, and seals the joint against contaminants that would otherwise cause fretting corrosion. Benefits That Matter to Manufacturing Engineers Increased strength and reliability: full-surface bonding significantly improves axial and radial load capacity compared to a mechanical fit alone. Looser machining tolerances: a slip fit combined with retaining compound can replace a heavy press fit, cutting machining cost and reducing installation stress on parts. Reduced fretting corrosion: eliminating micro-movement and sealing against moisture extends component life significantly. Simplified assembly: looser tolerances mean parts can often be assembled without heating, cooling, or heavy press equipment. Fewer secondary fasteners: retaining compound can replace keys, splines, and set screws in many cylindrical assemblies, reducing part count and complexity. Temperature Range Is Part of the Selection Criteria Too Strength grade and viscosity aren't the only variables that matter — continuous operating temperature affects which formulation holds up over the assembly's service life. Standard retaining compounds are rated for moderate continuous temperatures, typically up to roughly 150°C, while specialized high-temperature formulations extend that range considerably for applications near engines, exhaust systems, or industrial ovens where ambient heat alone can soften a standard-temperature product over time even without any external load pushing the joint toward failure. Specifying a retaining compound without checking its continuous-temperature rating against the actual thermal environment is a common reason an otherwise well-chosen strength grade underperforms in service. Common Applications Across Industries Bearing retention in automotive and heavy-equipment assemblies, rotor-to-shaft bonding in electric motors, cylinder liner retention in engines, and pulley or gear mounting on shafts in industrial machinery all rely on this same principle: converting a mechanical fit into a full-contact bonded joint improves both strength and longevity without adding weight or part count. Viscosity Selection…