Adjustable end wrench
An adjustable spanner is any of various styles of spanner (wrench) with a movable jaw, allowing it to be used with different sizes of fastener head (nut, bolt, etc). An adjustable spanner is an open-ended wrench with a moveable jaw. Its function is the same as any regular spanner - to grip fasteners, such as nuts and bolts - however, only adjustable spanners can grip fasteners of all sizes, thanks to their moveable jaw.