I have modified the box to work with magnets, because I didn't trust the printed rod, knowing how my printer performs with those from previous prints. ;)

Holes are for 6 x 3 mm magnets (6 diameter, 3 high).

Pretty cheap 6 x 3 magnets from Amazon:
https://www.amazon.de/gp/product/B07D33PG7Y/ref=as_li_ss_tl?ie=UTF8&linkCode=sl1&tag=smashdde-21&linkId=cc9fd061f52572899525bffe8a214028&language=de_DE

*The used link is a so-called affiliate one. When you buy the product using this link, I will receive a small provision. The price itself does not change. Thanks for your support :)