Remixed version of the design by Arctik Engineering . The original version is a bit too wide for the upper connection on Sodastream Crystal carbonators. I reduced the width in order to get enough clearance. This will make the nut less suitable for wrenches (although in my experience hand tightening is more than enough) but should fit Sodastream Crystal now.
A different and slimmer design by Jack printed well, but I wasn't able to get enough clamping force on the connection. I believe this is caused by the sub-optimal placement of the opening that is used to feed the hose through the nut. But maybe that version works better for you.
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Best printed in materials like PETG for slightly better layer adhesion. If you still experience layer separation thinking about the print direction/ placement on the builtplate (orthogonal or diagonal to the screw threads) might help.
The author remixed this model.
Slimmed down the outer casing of the nut in order to make it fit on the 90° angle that is present on the Crystal variant of SodaStream carbonators.