Open-ended, or "C" spanner wrenches are the most common type of spanner wrench. They are usually two-sided, with jaws on each end sized to fit a particular size of nut or bolt-head. Sometimes, they will be double-sided. The jaws are usually set at about 15 degrees from the run of the shaft. This type of spanner wrench is the easiest to use, providing the quickest and easiest access to a fastener. However, it is not very good for use with tight fasteners, as it only grips them from two sides.
Obstruction spanners are ideal for use in tight, enclosed spaces. An obstruction spanner has a head that is set at a sharper angle to its shaft than other types of spanners. This angle can be as much as 90 degrees.
Ring spanners have completely enclosed heads, with between six and 12 flats inside of the rings. These spanners grab onto the corners of the fastener's head and are very versatile, as they can adjust both hexagon and square bolts. They provide much stronger grip than open-ended spanners.
Combination spanner wrenches have one open end and one ring end. These are very useful on both tight and loose fasteners.
Split Ring Spanners
A split ring spanner wrench is basically a ring spanner with a section of the ring removed. It combines the desirable features of the open end and ring spanners.
Bulldog spanners, also known as crescent wrenches, look like one-sided, open-end wrenches except one of their jaws is movable. The movable jaw is manipulated using a worm screw located just below the end, allowing you to change the width of the jaws, which makes the spanner's compatible with many sizes of fasteners.