This is a side-release buckle or parachute buckle that works with 3/4 inch straps or 'webbing'.
I modeled this so I could print a replacement for a broken clip on my pack. Originally printed in PLA, which has been surprisingly functional so far, but I've reprinted in PET+ which has a much better flexible quality to it and should last far longer.
Prints best with support everywhere, especially for the female side of the buckle.