A NIKATTO groove joint plier is a type of adjustable plier commonly used for gripping and turning various objects, particularly in plumbing, mechanical work, and general household applications. The key feature of these pliers is their adjustable jaw size, allowing them to accommodate different sizes of objects. The plier's jaws consist of two parts: the fixed jaw and the sliding jaw, which can be adjusted along a series of grooves or positions. By adjusting the sliding jaw, you can open or close the pliers to fit different-sized objects. When using groove joint pliers, you can set the jaw size to match the object you want to grip or turn, and then you can lock it in place using a locking mechanism or a slip joint. 

This feature enables you to use the same pliers for various tasks, making them versatile and handy for many applications. Groove joint pliers are commonly used to grip and turn pipes, nuts, bolts, and other irregularly shaped objects. The serrated jaws provide a secure grip, which is especially useful when dealing with slippery or stubborn materials. These pliers are available in various sizes, with larger ones offering more substantial gripping capacity. They typically have cushioned or dipped handles for comfort during extended use.