3D printed keychain has two 15T gears that interlock and spin freely.

Uses 2x heat-set inserts with m3x10mm bolts to hold gears in. May work with 12mm.
Put a drop of threadlocker or super glue in the thread to stop it coming loose, don't overtighten or the gear won't spin properly.

Spinning these gears is addictive. Excellent as a fidget toy for tinkerers like me or as a focus for anyone with ASD.

If you've never had a compact interactive keychain like this before, give this gear a spin.

Suggest printing 0.15-0.2mm, no support, no brim.