For manufacturers, engineers, and maintenance professionals, the security of a threaded assembly is paramount. Fasteners must withstand constant vibration, thermal expansion, and mechanical shock without loosening. While mechanical locking devices like lock washers and split pins offer some resistance, they can be unreliable and costly. Threadlockers, or anaerobic adhesives, are the chemical solution to this problem, providing a robust and reliable lock that prevents self-loosening and corrosion. However, choosing the right threadlocker is a critical decision, as each type is engineered for a specific purpose.

This guide provides a professional overview of the different threadlocker types, exploring their strengths, common color-coding, and practical insights to help you select the ideal product for your application.

How Threadlockers Work

Threadlockers are unique liquid resins that cure into a solid plastic when exposed to metal ions in the absence of air. This anaerobic curing mechanism allows the adhesive to remain liquid during application, filling the microscopic gaps between the threads. Once assembled and deprived of air, the adhesive cures to form a durable, thermoset plastic that locks the threads together, providing a high degree of resistance to vibration and shock.

The strategic value of a threadlocker lies in its ability to create a full-contact, unitized assembly, preventing not only loosening but also protecting against rust and fretting corrosion.

The Main Types of Threadlockers by Strength

Threadlockers are categorized by their strength, which is typically indicated by an industry-standard color-coding system. This system provides a quick and reliable way to identify the intended application for each product.

1. Low-Strength (Purple)

Low-strength threadlockers are designed for small fasteners that require frequent disassembly. They provide a secure lock that prevents loosening from minor vibrations while still allowing for easy removal with standard hand tools.

• Key Characteristics: Low break-away torque, easy to remove, good for small-diameter fasteners (up to M6).
• Best for: Delicate assemblies like set screws in electronics, eyeglasses, carburetors, and other components where future maintenance is expected.

2. Medium-Strength (Blue)

Medium-strength threadlockers are the most versatile and widely used type. They offer a reliable hold for fasteners that may need to be disassembled for maintenance or repair in the future.

• Key Characteristics: Secure bond that withstands moderate vibration and shock, removable with standard hand tools.
• Best for: General-purpose industrial applications, such as machine tools, pumps, compressors, and mounting bolts where routine servicing is required.

3. High-Strength (Red)

High-strength threadlockers are considered “permanent” and are designed for critical, high-vibration applications where the assembly is not intended to be disassembled. They provide the highest level of resistance to loosening.

• Key Characteristics: High break-away torque, requires localized heat (typically over 250°C) and hand tools for removal.
• Best for: Permanent assemblies in heavy equipment, structural bolts, engine components, and any application where failure is not an option.

4. Wicking Grade (Green)

Wicking grade threadlockers are unique low-viscosity formulas that are applied after the assembly has been torqued. They are able to penetrate and wick into the pre-assembled threads, locking the fasteners in place.

• Key Characteristics: Low viscosity, fast wicking action, typically high strength, permanent.
• Best for: Locking and sealing pre-assembled fasteners like set screws and electrical connectors, or for sealing porous welds and castings without disassembly.

Actionable Advice for Professionals

Choosing the right threadlocker requires careful consideration of your application’s requirements.

1. Match Strength to Application: The most critical decision is selecting the right strength. Never use a high-strength threadlocker on a small fastener that may need to be serviced, as this can lead to fastener damage.
2. Consider the Environment: For applications with exposure to high heat, a high-temperature-resistant formulation is essential. For oily surfaces, an oil-tolerant threadlocker is required to ensure a reliable cure.
3. Proper Surface Preparation: For optimal performance, always ensure threads are clean and free of grease and oil.
4. Understand Removal Methods: Be aware of the removal process for each threadlocker type. Blue can be removed with hand tools, while red and green require heat.

Incure: Your Partner in Threadlocking Solutions

At Incure, we understand that the integrity of your threaded assemblies is the foundation of a safe and reliable operation. Our Re-Lok™ series of anaerobic adhesives offers a comprehensive range of high-performance threadlockers, each engineered to meet the specific demands of your projects. From low-strength formulas for small screws to high-strength, high-temperature solutions for heavy equipment, our products provide the confidence and security you need. Our team of technical specialists is dedicated to collaborating with you to select the precise threadlocker that will secure your components and enhance the longevity of your products.