Find the exact center of round, square, hexagon, and octagon shapes in only seconds. For example, place a round disc within the 60 degree or 90 degree flange. With a scriber or other pencil, mark along the scribe line. Then turn the discs 90 degrees and mark again. The 2 intersecting lines are the center of the disc. The others shapes require a slightly different procedure, clearly outlined in the included instructions. Use with circles, octagons, and squares up to 8" and hexagons up to 5 3/4". Constructed from clear plastic.