Micro-Mark - All Scales - Tools - Yardstick Compass (SKU 109-14302)
Slip these trammel points on any standard size yardstick and draw arcs and circles up to 72 inches dia. Use a longer stick the same width and thickness as a yardstick and draw circles as large as you like. All aluminum except steel point. 3-1/2 inches long. Great for laying out model railroad curves.
Fits yardsticks from 1-1/8" to 1-1/4".