I am upgrading the build platform on my Prusa and liked the thumbwheels from HBP Quick Leveler Redux, but I needed some to fit M4 nuts. So I decided to write a parametric OpenSCAD script to make thumbwheels of any size. The included stl is for an M4 nut.
If you need M4 thumbwheels, use the included stl and make as many as you need using multiply in skeinforge. If you need a different size, download the .scad file and have fun. I included lots of comments to hopefully make it easy.