Which type of pliers is characterized by an adjustable locking mechanism?

Locking pliers, also known as Vise-Grips, are designed with an adjustable locking mechanism that allows them to securely clamp onto objects. This feature provides a strong grip, which can be especially useful in situations where hands-free operation is needed, as it allows the user to apply pressure without having to continuously hold the handles together. The locking mechanism can be adjusted to fit various sizes of materials, making locking pliers versatile in a range of applications, including holding, twisting, and turning.

Other types of pliers mentioned in the options, such as needle nose, flat-nose, and side-cutting pliers, do not have this locking feature. Needle nose pliers are designed for precision work in tight spaces, flat-nose pliers are used for gripping and bending, and side-cutting pliers are mainly intended for cutting wires. Each of these tools serves its specific purpose but lacks the ability to lock in place, which distinguishes locking pliers as the correct answer.