For use with M3 double nuts used as fasteners.I use it for the spring-loaded bed-leveling double-nuts on my prusa mendel 3d printerYou can tighten/loosen one or two nuts at a time. Usually in such fasteners, one nut sets the tension and the second nut is used as a lock nut.Tags: accessory bed finger level M3 mendel nut printer prusa rosette thumb thumbwheel wheelThere are a bunch of these out there, but I couldn't find one that dealt with double nuts. You only need one of these instead of 4 used in other designs where the nut is fused into the thumbwheel.The .scad file is also attached so you can make changes to work with other types of hardware and/or improve this design as you see fit!Enjoy!