My last printed carabiner kept popping off so I came up with this design with a nut to lock it closed.
I designed this to replace the round carabiner that I created for my pet waste bag roll dispenser:
UPDATE: I uploaded version 4 to add thread stoppers for a better feel.
Once printed, you need to bend the long threaded end out just enough to screw on the nut. For this reason, ABS or PETG may be the better choices of filament but it's doable with PLA Pro and should be with PLA too. Once you get the nut in place, you can let it take it's natural shape and just open and close it by twisting the nut.