A bicycle storage box and a retractable fender designed for small-wheel bikes—both can be 3D printed. However, to ensure smooth, effortless extension and retraction, the fender needs to be properly bedded in after assembly. If you’d like to simplify the process, you can simply scale down three smaller units proportionally; just be sure to carefully measure the length—while it’s no problem to make them small enough for proper extension, the fender may become loose once fully extended. After inserting the pivot shaft, secure it with adhesive, or alternatively use wire; you can also print 0.2‑cm thick spacers and bond them to both ends of the fender.