Double box end wrench flat

They are usually sold in sets like other, similar to other wrenches. The closed-ended side is designed to loosen tough nuts, while the open-ended side is used to unscrew it quickly. See Also: 10 Best Combination Wrench Sets. The flat jaws of these wrenches are slid around nuts or bolt heads and levered for loosening or tightening. The open ends allow the tool to be slid over the nut in tight quarters where there would be insufficient space for a box wrench or a socket, or where the length of a shaft or pipe interferes.