A "Maulschlüssel," also known as a "box wrench" or "open-end wrench," is a hand tool used for gripping and turning nuts and bolts. It features a U-shaped opening at one end, which fits over the fastener, allowing for torque application. The other end may have a closed loop that fits snugly around the nut, providing a secure grip. These tools come in various sizes to accommodate different fastener dimensions. They are commonly made from steel for durability and can be found in both metric and imperial measurements. A toolbox often contains several sizes of Maulschlüssel for versatility in mechanical tasks.