Useful For Scribing Parallel Lines, Circles and Arcs. Allows any size circle or arch to be made either with a steel rule or length of wood. Fast set up and allows for quick and accurate setting out and marking. Knurled screws Width 3/8"(10mm) to 1-1/4"(32mm). Pencil Holder in one piece to mark your work. Radius Lengths as required with your own made beam.