Nuts can be tightened or loosened with nut pliers. The jaws are adapted to the shape of the nut. They grab the nut on four of the six faces. Unlike wrenches, the jaws don't move parallel. Sometimes they are ribbed on the inside for a better grip and the opening can be fixed with a set screw. The pliers cannot then be closed further than the screw allows, so that excessive pressure cannot be exerted on the side surfaces of the nut and thereby damage them.
See also combination pliers. [MOT]