There is no single ideal threadlocking compound. The right choice is the one that matches a specific application. Threadlockers are anaerobic adhesives that keep threaded fasteners from loosening under vibration, shock, or thermal cycling, and that seal threads against corrosion. Which grade fits depends on the joint.

Strength Grades and the Color Code

Threadlocking compounds are categorized by strength, meaning the torque needed to break the bond and disassemble the fastener. Industry practice uses a color code:

Low Strength, Typically Purple

For small fasteners, roughly under 6 mm, that need frequent adjustment or easy removal without thread damage. Holds against minor vibration and releases with standard hand tools. Common on calibration screws, set screws, optical instruments, and small electronic assemblies.

Medium Strength, Typically Blue

The general-purpose grade. Secures fasteners that need to stay put but may be disassembled occasionally with hand tools. Strong resistance to vibration and shock, with a bond that breaks without extreme effort. Common on machine tools, pumps, compressors, and motor mounts.

High Strength, Typically Red

For permanent assemblies where maximum locking is required and disassembly is rare or reserved for overhaul. Resists severe vibration, shock, and chemical exposure. Disassembly typically needs localized heat, often 250 degrees C or higher, plus significant force. Common on heavy equipment, engine and transmission components, and large studs.

Wicking Grade, Typically Green

Low-viscosity, medium-to-high strength, designed to penetrate pre-assembled fasteners by capillary action and to seal weld porosity and castings. Useful when parts cannot be disassembled to apply adhesive.

Beyond Strength

The right compound also depends on:

• Substrate material: most threadlockers cure well on active metals such as steel, brass, and copper. On passive metals such as stainless steel, aluminum, or plated surfaces, a primer or activator is often needed for adequate cure speed and strength.
• Temperature resistance: standard grades handle roughly 150 degrees C. High-temperature formulations extend to around 230 degrees C or more.
• Chemical resistance: consider exposure to oils, fuels, and coolants. Most grades resist these well; specialized formulations offer more.
• Viscosity and gap: choose a viscosity that flows into your thread pitch and any gap.
• Cure speed: fixture time and full cure affect throughput and depend on temperature and metal type. Activators accelerate cure.
• Application method: liquids are standard, but sticks, gels, and tapes suit overhead work or lower-mess assembly.

Selecting a grade is a matching exercise between strength, removability, environment, and cycle time. Email Us to review your fastener sizes and service conditions with Incure’s technical team.

A Selection Workflow

1. Ask whether the fastener will ever need disassembly in service. If yes with hand tools, start with medium strength. If no, or only at overhaul, consider high strength.
2. Size the grade to the fastener. Very small fasteners take low strength; large, high-stress bolts take high strength.
3. Check the substrate. Passive metals or plating means planning for an activator.
4. Check the service temperature and chemical exposure, and step up to a high-temperature grade if needed.
5. Confirm cure speed fits your line rate, and add an activator if the shop runs cold.
6. Standardize where practical on a small set of grades to simplify inventory and training.

Surface Preparation and Dispensing

Even the right grade underperforms on a poorly prepared thread. Clean male and female threads with a residue-free solvent to remove cutting oil, rust preventive, and dust, and let them dry. For a through-hole, apply a few drops of threadlocker down the female threads in the engagement zone, then run the fastener in. For a blind hole, apply to both the bolt and the bottom of the hole so trapped air is pushed out ahead of the adhesive as the bolt seats. For a pre-assembled joint that cannot be taken apart, use a wicking grade applied at the nut-to-bolt junction and let capillary action draw it in. Assemble to the specified clamp load promptly, since the cure begins as soon as air is excluded.

Common Specifying Mistakes

• One grade for every fastener: a single medium grade across a machine ignores small adjustment screws that need low strength and critical structural bolts that need high strength.
• No activator called out for stainless or plated fasteners: the joint may not reach rated strength within the assembly window.
• No removal procedure in the service manual: a technician who does not know a red grade was used may strip the fastener trying to break it cold.
• Assuming full strength at fixture time: the joint holds handling loads early but should reach full cure before high service loads.

How Incure Supports Fastening Reliability

Incure supplies anaerobic threadlockers across low, medium, and high strengths, plus wicking grades, high-temperature options, and activators, with technical consultation to match a grade to your application, materials, environment, and serviceability requirements. We also advise on surface preparation, dispensing, and cure.

For related guidance, see how thermal expansion mismatch loads a fastened joint, our comparison of adhesive strength for heavy-duty repairs, and how cure speed varies across chemistries.

Summary

The right threadlocking compound balances locking strength, removability, environmental resistance, and production efficiency for a specific fastener. Work through disassembly needs, fastener size, substrate, and service conditions, and confirm cure behavior on your actual parts.

Contact Our Team to select a threadlocking compound for your assemblies.

Visit www.incurelab.com for more information.