EDIT: I added a V2 of the male buckle with more rounded corners and shorter pins. This makes it a bit easier to remove but also makes it a tad more prone to slipping out if the forces get too high - which obviously never happens if used for keys or something similar.

Also I tried a .4 nozzle which hugely improves the result. 

This is the tiniest buckle I was able to create as I was looking for something low profile to make my keys quick-release-able.

Can be printed with a .6 nozzle but the keyring loops need supports. Make sure to inpaint the seam to the back of the male buckle as bambu studio tends to place it along the sides which are exposed to some stress.

Best to print this in PETG.