What type of nuts are specifically referred to for external-wrenching applications?

The type of nuts specifically referred to for external-wrenching applications are plain hex nuts. Plain hex nuts are designed with a hexagonal shape that allows for easy gripping with wrenches, making them suitable for external wrenching. Their straightforward design and standard dimensions enable them to be used in various mechanical applications where a wrench can be applied externally for tightening or loosening.

In external-wrenching applications, these nuts are preferred due to their compatibility with standard tools, ensuring accessibility and ease of use. Their ability to handle high torque loads makes them reliable for securing components in assemblies.

While other types of nuts may serve different purposes, such as shear nuts which are specifically designed for applications concerning shear loads, and internally-wrenching nuts that require tools to grip from the inside, they are not intended for external wrenching scenarios. Barrel nuts also have a specific design that caters to unique applications, typically involving alignment features rather than general fastening where external wrenching is necessary. Thus, plain hex nuts stand out as the most suitable choice for external-wrenching applications.