Ring spanners are fixed size spanners with an enclosed opening used to grip nuts and bolts, the opening is often six-point or twelve-point  to grip hex heads but ones with eight-points are also available for nuts and bolts with square heads. Openings with twelve-points are use full where space is an issue as they can fit on the head at twice the angles the six-points can, the ends are also often offset between 10 ° and 45 ° to the handles to help improve access to the nut or bolt head.