Thread Lockers, Retaining Compounds and Anti-Seize
Short answer
- Threadlockers, retaining compounds, and anti-seize each address a distinct failure mode, so the chemistry must be matched to the application: threadlockers resist vibration-induced loosening, retaining compounds hold slip fits, and anti-seize prevents galling, corrosion, and seizure.
- Threadlockers come in low, medium, and high strength grades, while anti-seize comes in copper, nickel, and ceramic bases, with ceramic extending the upper temperature limit to 400 °C.
- Anti-seize lowers friction enough that torque should be reduced by 25–30% to avoid overstressing bolts, and mechanical locks such as prevailing-torque nuts, wedge-lock washers, and safety wire can replace chemical aids when contamination or frequent disassembly is a concern.
When a bolted joint loosens under vibration, a bearing seat slips, or a high‑temperature connection needs a reliable torque, the choice of chemical fastener aid becomes critical. The wrong aid can either fail to hold or, conversely, over‑tighten a joint, leading to premature failure.
What types of chemical fastener aids are there?
Fastener aids fall into three broad families: anaerobic threadlockers, retaining compounds for slip fits, and anti‑seize lubricants. Each family addresses a distinct failure mode, and each has its own preparation and performance requirements. The adhesives, sealants and chemicals catalog at KKM groups these products, but the engineer must still match the chemistry to the application.
How do threadlockers work and when should you use them?
Threadlockers are anaerobic adhesives – they cure only where metal surfaces exclude air. The monomer mixture remains liquid in the presence of oxygen, but as the threads are tightened the metal‑to‑metal contact creates an oxygen‑free pocket. Free‑radical polymerisation then proceeds, forming a rigid, resin‑filled thread that resists vibration‑induced loosening.
- Low strength (often labeled blue) – designed for fasteners that must be removed with hand tools. Typical shear strength is 30‑40 % of the bolt’s tensile capacity. Use on non‑critical adjustments, such as sensor mounts.
- Medium strength (often red) – provides 60‑70 % of bolt tensile strength. Requires a standard wrench for removal. This is the work‑horse grade for most machinery.
- High strength (often green or purple) – cures to a very hard bond, holding 80‑90 % of tensile strength. Removal normally needs heat (≈ 180 °C) or a special impact tool.
Key preparation steps:
- Clean the threads to a light oil‑free condition. Light oil (e.g., machine oil) can be left if the product is formulated for “oil‑tolerant” use, but heavy greases must be removed.
- For stainless steel, aluminum, or galvanized surfaces, apply a compatible primer. The primer contains a small amount of metallic oxide that promotes adhesion; without it, the anaerobic cure may be inhibited, leading to a weak bond.
- Apply the threadlocker sparingly – a thin film that fills the thread crevices is sufficient. Excess material can be squeezed out and create a brittle bridge that cracks under load.
Because the cure is anaerobic, a fastener that will never be fully tightened (e.g., a bolt left at a preliminary torque) will not cure properly. In such cases, a medium‑strength product with a faster cure time is preferable.
When should you use a retaining compound on a slip fit?
Retaining compounds are formulated for applications where a shaft must be held in a hub or bearing seat without a traditional interference fit. Unlike threadlockers, they do not rely on thread engagement; instead, they fill the annular clearance between two cylindrical surfaces and cure to a high‑strength bond that resists axial and radial loads.
Typical uses include:
- Keyless hubs on electric motors where a shaft is pressed into a hub and must stay put under torque spikes.
- Bearings that are pressed onto a shaft in a high‑vibration environment, such as gearboxes.
- Gear or pulley assemblies where a split‑ring is impractical.
Retaining compounds differ from threadlockers in two fundamental ways:
- Cure mechanism – Most are also anaerobic, but they cure in the narrow gap between the shaft and hub rather than between threads. The gap must be small enough (typically 0.01‑0.03 mm) to exclude air.
- Load profile – They are designed to carry shear and tensile loads across the entire contact area, not just the thread flanks. Consequently, the shear strength is often higher than a comparable threadlocker grade.
Installation tips:
- Ensure the mating surfaces are clean and free of rust, oil, or machining chips. A light solvent wipe is usually sufficient.
- Apply the compound evenly around the shaft circumference. For larger diameters, a brush or syringe helps achieve uniform coverage.
- Press the components together to the final position before the cure begins. Most compounds reach handling strength in 30‑60 minutes at ambient temperature, but full strength may require 24 hours.
For dimensional reference, see the bushings and hubs catalog, which lists the typical clearance ranges that retaining compounds are designed to fill.
How do anti-seize bases, temperature limits and torque compare?
Anti‑seize lubricants are solid‑film greases that prevent galling, corrosion, and seizure on threaded or bolted connections. The three most common bases are copper, nickel, and ceramic (often aluminum oxide or molybdenum disulfide). Each base has a distinct temperature envelope and compatibility profile.
- Copper‑based – Operates reliably from ‑40 °C up to about 315 °C (600 °F). Ideal for steel‑to‑steel or steel‑to‑cast‑iron joints where the copper particles will not contaminate the mating surface.
- Nickel‑based – Similar temperature range (‑40 °C to 315 °C) but chemically inert to stainless steel and many alloys. Nickel particles do not cause galvanic corrosion, making this the preferred choice for stainless‑steel bolts on stainless housings.
- Ceramic‑based – Extends the upper limit to 400 °C (750 °F) and provides excellent load‑carrying capability under high‑temperature cycling. The ceramic particles are electrically insulating, useful in applications where conductivity must be avoided.
Warning: Anti‑seize dramatically reduces the coefficient of friction (often to 0.1–0.15 of the unlubricated value). If the same torque setting is used as for a dry joint, the resulting clamping force can be 30‑50 % higher, potentially overstressing bolts or deforming components. The general rule is to reduce the torque by 25‑30 % when applying anti‑seize, then verify the clamp load with a calibrated torque wrench or a bolt‑tension measurement method.
Application guidance:
- Apply a thin, even film to the threads and the bearing surface. Excess can migrate into bearing races or gear teeth, causing wear.
- For high‑temperature zones, verify that the selected base exceeds the maximum service temperature by at least 20 °C to account for transient spikes.
- When re‑torquing a joint, re‑apply anti‑seize; the compound can be displaced after the first torque cycle.
Anti‑seize is often listed alongside other lubricants in the lubricants and lubrication systems catalog, but it is distinct from oil‑type lubricants because it remains in place after the joint reaches operating temperature.
What mechanical alternatives replace chemical fastener aids?
When chemicals are undesirable—due to contamination concerns, inspection constraints, or the need for repeatable disassembly—mechanical locking methods can provide comparable security.
- Prevailing‑torque nuts – These have a deformed or serrated thread that creates frictional resistance as the nut is tightened. The torque required to turn the nut exceeds the torque needed to loosen it, providing a self‑locking effect without any adhesive.
- Wedge‑lock washers (e.g., Nord‑Lock, split lock washers) – A conical washer is placed under the nut; as the nut is torqued, the wedge forces the washer into the threads, creating a prevailing torque effect. They are inexpensive and work on standard nuts.
- Safety wire – A stainless‑steel wire is twisted through pre‑drilled holes in the fastener head and a supporting structure. The wire must be tensioned correctly; otherwise, it can loosen under vibration. This method is common in aerospace and high‑reliability industrial equipment.
Mechanical methods have the advantage of being visible during inspection and do not require curing time. However, they may add bulk, require additional installation steps, or introduce stress concentrations. Selecting between a chemical aid and a mechanical lock often depends on the maintenance philosophy: if frequent disassembly is expected, a low‑strength threadlocker or a prevailing‑torque nut may be preferable; for permanent assemblies, a high‑strength threadlocker or a retaining compound is usually more efficient.
How do you choose the right fastener aid?
Before ordering any fastener aid, run through the following decision points. This checklist helps avoid common pitfalls such as using a high‑strength threadlocker on a bolt that must be removed with a hand‑tool, or applying copper‑based anti‑seize on a stainless‑steel joint where galvanic corrosion could occur.
- Is the joint subject to vibration or cyclic loading? → Choose a threadlocker grade that matches the required removal method.
- Are the mating surfaces plated, anodized, or otherwise inert? → Use a primer‑compatible threadlocker or a nickel‑based anti‑seize.
- Does the application involve a slip fit (shaft‑in‑hub) that will not be machined to a precise interference? → Retaining compound is the appropriate solution.
- What is the maximum service temperature? → Select copper, nickel, or ceramic anti‑seize accordingly, and verify that the temperature rating exceeds the peak by a safety margin.
- Will the joint need periodic disassembly? → Consider low‑strength threadlocker, prevailing‑torque nuts, or wedge‑lock washers instead of high‑strength adhesives.
- Are there contamination concerns (e.g., food‑grade, clean‑room)? → Mechanical locks or low‑outgassing, food‑grade threadlockers may be required.
For a full list of available products, browse the fasteners and hardware section, where you can cross‑reference nuts, bolts, and washers that are compatible with the chemical aids discussed.
If you need help identifying the right threadlocker, retaining compound, or anti‑seize for a specific assembly, feel free to reach out for sourcing assistance or cross‑reference guidance.
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Request a QuoteFrequently asked questions
What is the difference between a threadlocker and a retaining compound?
Threadlockers cure in threads and resist vibration-induced loosening, while retaining compounds fill the annular clearance between two cylindrical surfaces, such as a shaft in a hub or bearing seat. Most retaining compounds are also anaerobic but cure in a narrow gap, typically 0.01–0.03 mm, and carry shear and tensile loads across the entire contact area, so their shear strength is often higher.
How much should you reduce torque when using anti-seize?
Reduce the torque by 25–30% when applying anti-seize, then verify the clamp load with a calibrated torque wrench or a bolt-tension measurement method. Anti-seize dramatically reduces the coefficient of friction, so using the same torque as a dry joint can raise clamping force by 30–50%, potentially overstressing bolts or deforming components.
What temperature can copper, nickel, and ceramic anti-seize handle?
Copper-based and nickel-based anti-seize operate from –40 °C up to about 315 °C (600 °F), while ceramic-based extends the upper limit to 400 °C (750 °F). The selected base should exceed the maximum service temperature by at least 20 °C to account for transient spikes. Nickel suits stainless-steel bolts on stainless housings because it does not cause galvanic corrosion.
Why does a threadlocker need a primer on stainless steel or aluminum?
Stainless steel, aluminum, and galvanized surfaces need a compatible primer because the primer contains a small amount of metallic oxide that promotes adhesion. Without it, the anaerobic cure may be inhibited, leading to a weak bond. Threadlockers cure only where metal surfaces exclude air, so a thin film on clean threads, with heavy greases removed, is also required.