What is the function of the box end of a wrench?

The box end of a wrench is specifically designed to grip fasteners, such as nuts and bolts, from the sides. It has a closed, rounded shape that allows it to fit snugly over the corners of these fasteners. This design is particularly advantageous for gripping rounded nuts, as the box end can apply even pressure around the entire fastener, reducing the likelihood of stripping or damaging it compared to other types of wrenches.

Using the box end is beneficial when working with fasteners that have been rounded off or are damaged, as it can provide more surface contact than an open-end wrench. This ability to firmly grip the sides of a rounded nut helps mechanics effectively turn them without slipping.

While the functions of tightening screws, fitting over various sizes of bolts, and breaking loose rusted bolts may be relevant to other types of tools or wrenches, they do not specifically describe the primary purpose of the box end of a wrench. The box end excels in secure grip and torque application, making it a vital tool for working with fasteners effectively.