Above 3d printed part will allow to repair a broken Nut on a Soda Stream Crystal and others.
This Repair uses a standard brass / metal 6mm union nut with M10x1 Thread.
The Nut can be bought for less then 1 eur / usd.
Plus - this small 3d printed adapter is needed - see photos and files.
I printed the part in PetG with 0.16 Layerheight and used enough wall loops to get a solid part.
One Version includes a sort of brim that is easy to cut away after printing - the other one without.

This allows a very solid repair - at your own risk.
there are other approaches that replace the entire nut - see:
https://www.thingiverse.com/thing:7040417
https://www.thingiverse.com/thing:4783847