Summary

This is a holder for micro bits (4mm across flats, e.g. WOWStick or Wiha precision screwdrivers).

When slicing, you'll have to place the object upside down and then configure your g-code to pause the print at a certain layer and insert 12 6x3mm magnets (possibly with some super glue) and then resume the print. You can see that in the photos.

There are additional magnet slots at the sides so you can combine several of these into one block.

Designed in Fusion 360, you can get the model here: https://a360.co/31WeWXs