In the fastener industry, the terms prevailing torque lock nut and all-metal lock nut are often used interchangeably. While they’re closely related, they are not exactly the same thing. Understanding the difference can help avoid confusion when reviewing specifications, sourcing parts, or selecting the right fastener for an application.

At the most basic level, a prevailing torque lock nut is any lock nut designed to resist loosening by creating friction between the nut and bolt threads before the nut is fully tightened. The resistance created during installation is known as prevailing torque. This added friction helps the assembly maintain clamp load and resist loosening caused by vibration or movement.

An all-metal lock nut, on the other hand, refers specifically to the construction of the nut itself. As the name suggests, all-metal lock nuts contain no nylon or non-metallic inserts. Instead, the locking action is created by intentionally distorting or crimping a portion of the nut near the top threads. As the bolt is tightened into the nut, the distorted portion creates resistance during installation, generating the prevailing torque that helps prevent the fastener assembly from loosening due to vibration or movement.

Most all-metal lock nuts are considered prevailing torque lock nuts because their design creates resistance during installation. However, not all prevailing torque lock nuts are all-metal. Nylon insert lock nuts also create prevailing torque through friction generated by the nylon insert. The locking method is different, but the functional principle is the same.

In simple terms:

  • Prevailing torque describes how the nut locks
  • All-metal describes what the nut is made of

That distinction matters because material construction directly affects where the fastener can be used.

All-metal lock nuts are commonly selected for high-temperature or demanding industrial environments where a nylon insert lock nut might exceed its temperature rating. Applications involving heat, chemicals, or heavy vibration often favor all-metal designs because they maintain locking performance without relying on non-metallic components.

Common applications for all-metal lock nuts include:

  • Heavy equipment
  • Automotive applications
  • Industrial machinery
  • Structural assemblies
  • Exhaust and high-heat environments

Nylon insert lock nuts remain widely used across many industries because they are cost-effective, reusable in some applications, and provide reliable vibration resistance in moderate environments. However, because the nylon insert is temperature rated, these lock nuts may not be recommended for high-heat applications or environments involving certain chemicals.

When reviewing fastener specifications, it’s important not to assume the two terms mean exactly the same thing. A specification calling for a prevailing torque lock nut may allow either a nylon insert or an all-metal design depending on the application requirements. If temperature resistance, durability, or material compatibility are critical, confirming the exact lock nut style becomes especially important.

Understanding the difference between prevailing torque lock nuts and all-metal lock nuts can help buyers and sourcing teams select the right fastener for the application. Earnest Machine stocks a wide range of industrial fasteners, including serval different types of all-metal and nylon insert lock nuts. Whether you need help locating a specific fastener or sourcing a hard-to-find item, our team is ready to help. Contact Earnest Machine at 800-327-6378 or [email protected].