This is a form-locking adapter for M42 and T2 manual lenses from my GuerillaBeam project.It works by snapping into the obligatory undercut of the M42 screw thread, and can be positively locked with a female screw.Designed to fit on a GuerillaBeam projector, it might be usable for other projects. I regularly print this on my Ultimaker in PLA with 0.3mm layer height with 60mm/s though it looks better with 0.2mm.Please visit my crowdfunding for GuerillaBeam: https://www.indiegogo.com/projects/open-source-guerillabeam/x/5613022