Pin spanners, also known as ‘pin keys,’ work in a slightly different way to the other spanners in this guide. Rather than gripping the head of a fastener around the outside, they grip the fastener by inserting two metal pins into special holes in the fastener head.
The fasteners that pin spanners are used on are called ‘lock nuts’ and are most commonly used to attach abrasive grinding pads to grinder power tools. When the spanner is turned, the moving pins cause the fastener to move too.
Pin spanners come in a few designs that all achieve the same results. Some have a pair of jaws with one pin on each jaw, others have no jaws and some are adjustable.
Adjustable pin spanners can be adjusted using an adjustment screw or by inserting one pin and opening the tool up to fit the second pin.
Many pin spanners have a hole for attaching a lanyard to or for joining multiple tools together.
A minimum of two sizes will be given in the product description: the diameter of the pins and the distance between the centre of one pin and the centre of the other. The diameter of the pins is usually 3mm, 4mm or 5mm and the distance between the pins ranges from 20mm to 35mm.
Occasionally, pin spanners will have an extra feature such as a stepped hole for turning flat-sided fasteners. These are fine for occasional use but otherwise you are better off investing in a ring spanner.