I always lose these belt loop keepers which retain your pants' belt, so made a customizable one in OpenSCAD. It requires BOSL2 for those nice bevels.

Changeable parameters:

BELT_WIDTH the width of your belt

BELT_THICK the thickness of your belt

LOOP_WIDTH how wide the keeper should be

LOOP_THICK how thick the keeper should be

ADJUST to adjust for tightness (the default 1 mm should be just fine).