A two-piece tool, forming a beam compass, used to layout circles or arcs. Often a length of 1x stock is used as the beam, which becomes the radius. One piece has a point which becomes the center, the other has a pencil which marks the circumference.
https://www.micromark.com/Web%20Store%20Images/83187_R.jpg
https://www.micromark.com/Web%20Store%20Images/83187_R.jpg