Hello! This is a simple hand tool to cut circles. You can adjust the distance from 10mm to 100mm, with 1mm increments. A gradation indicates the distance of the needle to the blade, but use a ruler to verify the radius. It uses a standard hobby blade (x-acto) that slides into a slot. It's press-fit for me, but if the blade is slightly loose, you can glue it in place to make sure it doesn't move. To install it, insert a nail in the blade's oblong hole and push it through. To install the needle, cut a pushpin and fix it in the needle-holding part using crazy glue. To print the parts on a FDM machine, it's better to place them all in an upright position (like they are on pictures). Update: new blade cover addedhttp://www.thingiverse.com/thing:192308 Also, be careful using it as a tool! use at your own risk! Enjoy!