Cupid's Bowden Coupler

Two fancy magnetic couplers and a fixed one, they take PC4-M10 push in connectors and 6x3mm magnets, you better dry your filaments before you print these, there's some gnarly overhangs in the fancier ones.

“Heart to heart” - Simple flat magnetic coupler, easy to print, either face up prints fine. Takes 6 6x3mm magnets (3 per side).

“Mender” - The broken heart, I printed the parts as they're placed in the file with no supports, there's a bit of a nasty overhang that will curl if your filament is damp, if you want extra safety add supports, if you want perfect threads lay the smaller piece so the hole faces straight up, they'll still be usable even when printed horizontally but they'll be rougher, need some cleaning. Takes 4 6x3 magnets (2 per side).

“Bypass” - Fixed coupler, nice and solid, single piece, needs no magnets, smaller than “Mender” and easier to print, but still keep your filament dry.

Print at .15 and lower layer height for functional threads.

Adding extra perimeters or infill doesn't seem to be necessary, printed some with 2 walls and 10% infill, some with 4 walls and 25% infill, none budged even when wrenching in those fittings with the finesse of a silverback gorilla.

When you put those fittings in, don't start screwing them too hard unless you're sure that they're going straight, once you're sure, wrench em in while pushing forward, don't be afraid to use some serious force. These couplers are tiny, you'll have to put em in a vice, or grasp them between the handles of a pair of pliers like I did.

I'm afraid I couldn't test how well the magnets fit as they aren't yet delivered from good ol China, hence why I just lifted the tolerances from another model I tested, its threads play nice even with my chinesium fittings, I'm sure the magnets will fit nice as well, check how thick your magnets are before putting them in, apparently they're sometimes thinner, may need some spacers.

Used this gentleman's threads and tolerances just to be sure, they seemed quite precise.