Thread-locking fasteners and security patches help improve joint reliability by preventing fasteners from loosening due to vibration, thermal cycling, and dynamic loads. However, these locking features also add friction during installation, making it harder to achieve accurate, repeatable torque.

Fasteners with pre-applied thread lockers or security patches require additional torque to overcome the friction created by these locking features. This resistance is known as prevailing torque and can significantly affect tightening accuracy if it is not properly measured and accounted for during the fastening process.

Understanding and controlling prevailing torque allows manufacturers to distinguish between the torque required to overcome thread friction and the torque required to achieve the desired clamp load. This results in more precise fastening, improved joint consistency, and fewer assembly defects.

What Is Prevailing Torque?

Prevailing torque is the resistance created by a locking feature as a fastener is installed. Unlike the torque used to generate clamp load, prevailing torque is consumed overcoming friction before the fastener can generate the desired clamping force.

Thread-locking compounds, nylon patches, and other locking features can increase this resistance. As a result, applying the same torque specification used for a standard fastener may not produce the same clamp load when a locking feature is present.

For manufacturers, this makes prevailing torque control an important consideration when establishing fastening specifications.

1. Understand How Locking Features Affect Torque

The first step in controlling torque on thread-locking fasteners and security patches is understanding how the locking feature affects the fastening process.

Common locking methods include:

• Liquid thread lockers applied to the fastener or threaded hole
• Nylon security patches applied to fastener threads
• Pre-applied thread-locking compounds
• Other mechanical or chemical thread-locking features

These methods increase friction during installation. The amount of prevailing torque can vary depending on the fastener design, locking material, application, temperature, and number of installation cycles.

Because prevailing torque can vary, simply applying the same torque specification used for a non-locking fastener may result in an incorrect clamp load.

2. Measure and Compensate for Prevailing Torque

To achieve consistent fastening results, manufacturers should measure the prevailing torque associated with the specific fastener and locking system being used.

The fastening process should account for the torque required to overcome the locking feature separately from the torque required to generate the desired clamp load.

In practical terms, the total applied torque can be viewed as consisting of:

Applied Torque = Prevailing Torque + Torque Required to Generate Clamp Load

Understanding this relationship allows engineers to establish more appropriate torque specifications for the application.

Whenever possible, test and validate using the actual fastener, locking feature, joint materials, and assembly conditions. This helps ensure that the torque specification accurately reflects the real-world fastening application.

3. Validate Torque Settings Before Production

Validate torque settings before implementing them on the production line. This is particularly important for applications using thread-locking fasteners or security patches because prevailing torque can introduce additional variation.

A torque validation process can help engineers determine:

• The amount of prevailing torque generated by the locking feature
• The torque required to achieve the desired clamp load
• Whether the specified torque range is appropriate
• Potential over-torque or under-torque conditions
• How repeated installations affect fastening performance

Validation helps establish a reliable fastening process rather than relying solely on a nominal torque value.

4. Select the Right Torque Control System

Accurate torque control requires more than simply using a calibrated torque tool. The fastening equipment must be capable of controlling the application according to the requirements of the joint.

For complex or sensitive assemblies, smart electric screwdrivers can provide advanced torque control and process monitoring capabilities.

Mountz smart electric screwdriver systems provide torque control and process-control capabilities designed to help manufacturers improve fastening consistency and reduce assembly errors.

These systems can support error-proofing disciplines and adaptive fastening strategies while allowing multiple fastening steps to be incorporated into a controlled workflow.

For applications involving sensitive or complex joints, this level of process control can help manufacturers achieve more consistent fastening results.

Preventing Over-Torque and Under-Torque

When manufacturers do not properly account for prevailing torque, they may encounter both over-torque and under-torque conditions.

If the torque specification is increased too much to compensate for prevailing torque, the fastener or joint may be exposed to excessive torque. This can result in damaged threads, stripped fasteners, or other fastening failures.

If prevailing torque is not adequately considered, the torque available to generate clamp load may be insufficient, potentially resulting in an under-tightened joint.

The goal is to establish a torque specification that accounts for the locking feature while still producing the required clamp load.

Building a Reliable Prevailing Torque Control Process

A successful fastening process should consider the entire joint, not just the torque value displayed by the tool.

Best practices include:

• Identify whether the fastener uses a thread locker or security patch.
• Measure the prevailing torque associated with the locking feature.
• Establish the required clamp load for the joint.
• Validate torque settings using production-intent components.
• Select a torque tool appropriate for the application.
• Monitor fastening results during production.
• Periodically verify tool performance and process capability.

By incorporating these practices into the manufacturing process, engineers can improve fastening consistency and reduce the risk of defects.

Improve Assembly Quality with Better Torque Control

Thread-locking fasteners and security patches provide important benefits for maintaining joint integrity, but they also introduce additional variables into the fastening process.

Prevailing torque control helps manufacturers account for the friction created by these locking features and establish a more accurate relationship between applied torque and clamp load.

When combined with proper torque validation, appropriate tool selection, and process monitoring, prevailing torque control can help manufacturers reduce fastening variation, improve assembly quality, and prevent costly rework and warranty issues.

Watch the Webinar

Learn more about torque control for thread-locking fasteners and security patches in the Mountz webinar.

Watch the Mountz Torque Webinar

The webinar explains how prevailing torque affects fastening accuracy and provides practical guidance for measuring, compensating for, and controlling prevailing torque in manufacturing applications.

Improve Your Fastening Process

Whether your application uses liquid thread lockers, nylon security patches, or other locking technologies, understanding prevailing torque is essential for developing a reliable fastening process.

The Mountz smart electric screwdriver solution is for process reliability and efficiency with intelligent fastening strategies and high-precision torque accuracy. To see our full range of products, shop our store. Contact us anytime to ask a question. To inquire about price, request a quote. If you’d like to see our equipment in person, schedule an appointment. To get the latest torque-related news, follow us on LinkedIn.