This part is a flat compass. That's right! You don't need a compass. The way this works is that you need pencils. One pencil starts at the center, and the other at wherever you want to specify your radius. To specify your radius, there is an inch wide and a centimeter side. To me, this tool will be even less frustrating than a compass since you don't have to constantly worry about your compass moving and therefore you messed up your circle. .2 mm with 5% infill will work awesome! In addition, use PLA.