A nice simple magnetic life counter, print one of each file, no supports necessary
Requires:
Qty 22 1/8"x 1/8" Rod magnets https://www.leevalley.com/en-ca/shop/hardware/rare-earth-magnets/magnets/rod/40076-rare-earth-rod-magnets?item=99K3800
Qty 2 5mm dia, 1/2" long Chicago Screws https://tandyleather.ca/products/chicago-screws?_pos=1&_psq=1293-02&_ss=e&_v=1.0&variant=34105065504899
(sorry, I like to buy local for my projects so I don't have any amazon links)
simply insert the magnets into the holes (Watch out for polarity!). mine press-fit in, but if you need, use a small amount of CA Glue. Then use the chicago screws to fasten the wheels to the connector. Magnets will align on the inside.
If you are more ambitious than I am, then use the pause at layer feature of your slicer to make the numbers a different colour!
Enjoy