What type of pliers is designed to turn bolts and nuts for fastening or loosening?

The appropriate tool for turning bolts and nuts for fastening or loosening is a combination plier, but the choice that specifically fits this task best is actually a crescent wrench.

A crescent wrench is an adjustable wrench designed to grip and turn nuts and bolts efficiently due to its jaw design that can be easily altered to fit various sizes of fasteners. Its function is specifically engineered for this purpose, providing the user with a firm grip to apply significant torque without slipping.

On the other hand, combination pliers primarily serve as a gripping tool and provide cutting capabilities. They are often used for twisting wires and holding small objects rather than applying the torque necessary for turning nuts and bolts.

The slip joint pliers can grip and turn objects as well, but they are not ideally suited for the precise and secure grip needed for fastening or loosening bolts due to the way the jaws are constructed.

Finally, needle nose pliers are specialized for precision work in tight spaces, making them unsuitable for turning larger nuts or bolts. They lack the necessary leverage and grip required for such tasks.

Thus, while combination pliers have various uses, a crescent wrench is specifically designed to turn bolts and nuts effectively.