Not my model but I'm gonna use it for a project and wanted to be able to reference it here.

You can buy the official Kadee one here.

Print with full supports.

Positioning

Center of the coupler should be 1 1/8" or 28.575mm above rails.

Additional material

• 2mm OD, 10mm Free-Length Spring made of 0.3mm Diameter Wire to keep it closed

• M3 12mm bolt

• M3 nut

• 1.5mm wire for the cut lever

Spring keeps the knuckles closed. To open them, the wire is rotated. For this to function, you must have it rigidly attached to the rotating piece but loose in the outer one - if you have it too rigid, just increase hole diameter in the outer one.