There are combination wrenches featuring two same-size openings; the open-end allows you to quickly apply low torque and the box-end allows you to apply final and greater torque. The openings are machined to precision for a perfect fit with nuts and bolts. The 12-point contact gives the box-end greater endurance. Urrea grip system. There are combination wrenches featuring two same-size openings; the open-end allows you to quickly apply low torque and the box-end allows you to apply final and greater torque. The openings are machined to precision for a perfect fit with nuts and bolts. The 12-point contact gives the box-end greater endurance. Urrea grip system.