Trammel heads are marking out tools primarily used to draw large circles or arcs. They are sometimes called trammel points, or trammels.
Together with a beam, usually made from wood or metal, trammel heads make up a beam compass. They are clamped a set distance apart onto the beam.
Trammel heads come in pairs. Usually, one trammel head holds a pencil or other marking instrument and the other holds a steel point which anchors the tool to the surface being marked.
They can be also be used with a metal or wooden ruler. This allows the trammel heads to be accurately set a specific distance apart. The distance between the trammel heads can be altered and will determine the size of the circle or arc that will be drawn.
The radius of the circle that can be drawn with trammel heads is limited by the length of the beam they are used with.
Trammel heads are usually made out of die-cast metals such as aluminium. This is because aluminium is lightweight, strong and resistant to corrosion, so trammel heads are likely to last a lifetime.
