Wheel for building Brio/Thomas compatible wooden trains (and probably other small vehicles, as well). This variation on the original is more rounded.
Follow these instructions for how to build axels and assemble the wheels themselves.
Find the latest versions of this and other related designs at https://github.com/ex-nerd/3d
The SCAD file (original at https://github.com/ex-nerd/3d) contains measurements from all of the popular wooden train brands, and will likely improve as I have more time (and get access to a printer).
Print both parts and glue them together onto a 3/32" brass axle, using a furniture tack with a 1/2" head. See link in description for more instructions.