3rd busted rigid coupler

So I am working on my first real project using my MPCNC that I think is nearing completion/calibration and was doing a test draw on some cardboard with a sharpie when (I believe, wasnt in the room at the time) the force of the downward pressure caused the rigid coupler to slip and crack (again, third one, I know, hercules). So, that being said, I have been looking into alternatives and am trying to decide which to go with. Have any of you replaced your coupler with something new and if so what did you go with?

New coupler or old one?

You can replace it with any coupler, rigid would be best. If you get a spring printer style make sure you pre-load the spring out of it. Not a big deal, just the common reprap style usually do not fit a 5/16" screw well enough.

If you are having such issues with downward force, switching to something more solid will only cause something else to fail or be under high tension/pressure. Maybe adjust your tool path or starting height to put less pressure on the tool.

By pre-load spring, do you mean stretch it out?

yes, just a tiny bit of stretch.