For a christmas present, I made a coin vault. But I needed a simple lock that would fit into the 40mm hole my Fresnel drill could make. So, I designed this. After a first print, I thickened the outer ring radially and also increased the thicknesses some. Since pulling out was a little bit tricky, the locking piece's peg was given a "waist" to give a better grip in the last version.

After printing, a little bit of filing to smooth the locking lugs of the disk and... voila! a simple but effective lock that can be set into a standard hole and prevent coins from escaping.