This is the clip side of one of Arcade's Adventure stretch belts. I believe they have updated their buckle but if you happen to have this style and it broke, here's the fix. Mine broke and while Arcade is an awesome company and sent me a complete replacement belt, I didn't feel good throwing away the old belt, so I drew this up, and it has been working well for months.

I printed mine in PETG because I wanted transparent to match my broken buckle. It has held up well although I'd rather of used ABS/ASA/PC or some other stronger filament if I had them in the color I wanted.

I used Generic PETG @.2mm with something like 5walls, floor layers and top layers so it would be a solid part with no gaps in the infill.

This buckle works as is, although I've uploaded the .3mf file in case anyone wants to modify it.