This buckle is originally made for a replacement. The width of a strap should be around 16mm or less. I assume you could just scale it up if you have a wider strap. You can print this with no supports (and if you print with them, I'd recommend only using them for the parts shown on the last 2 screenshots). The main issue you might get is the buckle being broken on layers if your layer adhesion is bad (you will not have any issues with it if you've done temperature towers with your filament).

//In my case OrcaSlicer added some random line particles so I had to sand the buckle a bit, but you probably would not get stuck with this.

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[+]Printed Under The Settings:

Infill: 10%
Infill Type: Gyroid

Number of walls (wall loops): 3
Top shell layers: 4

Supports (optional): Tree (manual)

Ironing (optional): Topmost surfaces
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