It’s a sinking feeling: you’ve done everything right—you applied the threadlocker, waited the required time, and yet, the next day, those critical screws are loose, or worse, have fallen out completely.

You relied on a thread-locking adhesive to provide a secure, vibration-proof hold, but now your assembly is failing, and your project is at risk. If you’ve ever posted to a forum asking why your screws are still shaking loose despite using threadlocker, this guide is for you.

This common failure usually isn’t a fault with the concept of threadlocking, but rather an issue with product selection or application technique. We will break down the top reasons this happens and recommend the right Incure Re-Lok™product to keep those fasteners locked down for good.

Why Threadlocked Screws Still Fail (The Top Three Reasons)

When threadlocker fails to retain screws, it means the bond strength is lower than the forces (like vibration or thermal expansion) acting on the fastener.

1. The Wrong Strength Grade Was Used (Underspecified)

The most frequent error is matching the wrong strength of threadlocker to the application’s stress level.

• Light Duty (Purple) Threadlockers are designed for small, low-stress screws (e.g., set screws, instrumentation) that need occasional adjustment. If you use this on a high-vibration engine bolt, it will fail.
  
• Medium Duty (Blue) Threadlockers are for general-purpose applications up to 3/4″ (20mm) and are removable with hand tools. They are excellent, but they are not designed for extreme, high-impact forces or critical structural components.
  
• If you used Blue or Purple, but the screw still fell out, you need a higher-strength product.

2. Surface Contamination Prevented Full Bond Strength

A partial cure, often due to poor cleaning, results in a weak bond that can look cured but is structurally brittle or soft.

• Residual Oils: Any cutting fluids, anti-seize compounds, or heavy machining oils remaining on the threads act as a barrier, preventing the adhesive from achieving full contact with the metal.
  
• The Result: The threadlocker forms a weak, compromised film instead of a solid, tenacious thermoset plastic. The first significant vibration or shock will break this weak bond, leading to looseness.

3. Gap Size Exceeded the Product’s Capacity

Threadlockers are designed to fill the microscopic gaps between mated threads.

• Large Gaps: If the threads are heavily worn, the screw is too small for the hole, or if you are trying to seal a pipe with loose threads, the gap might be too large for a standard liquid threadlocker to bridge effectively.
• The Result: The adhesive may cure partially but lack the shear strength needed to resist the high lateral forces of a loose-fitting assembly, causing the screw to walk out.

The Incure Re-Lok™ Solution: Stepping Up to Maximum Retention

When medium-strength threadlockers fail, it’s time to upgrade to a heavy-duty solution that is specifically engineered for critical, high-stress, and high-vibration applications.

For screws that persistently shake loose, we recommend the Incure Re-Lok™ B72 Red Threadlocking Adhesive (Heavy Duty).

Summary of Best Practices for Total Security:

1. Clean Aggressively: Use a clean, residue-free solvent to thoroughly clean and degrease both the screw and the hole before application. Let them dry completely.
   
2. Use the Right Grade: When vibration is the issue, skip Blue (B43) and go straight to Red (B72) for a secure, permanent lock.
   
3. Apply Properly: Ensure the threadlocker is applied to the threads that will be fully engaged inside the assembly to guarantee an anaerobic cure.

By following these steps and upgrading to the high-strength Incure Re-Lok™ B72, you can confidently eliminate screw failures, even in the most demanding environments.