I lost my fuel cap during a night ride so I designed and 3D printed a new one. Designed in OpenSCAD with the threads.scad library by Dan Kirshner. Printed in PLA+. I wasn’t sure if the PLA would hold up against gasoline but so far, so good. My printed version is a little different design than the STL file here. I had planned on reprinting to this final design but the cap has held up so well that I haven’t bothered.
This design is on printables as well.