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…