Micro-Mark - All Scales - Tools - Yardstick Circle Cutter (SKU 109-82966)
Slip these trammel points on any standard size yardstick and cut arcs and circles up to 72 inches in diameter. Use a longer stick the same width and thickness as a yardstick and make circles as large as you like. Made of aluminum with steel point and blade. 3-1/2 inches long. Great for laying out model railroad curves and cutting templates.
Fits yardsticks from 1-1/8" to 1-1/4".