This is a replacement cap for Sodastream CO2 bottles. It has a little bit of knurling to help pull it back off, and it has indexing ridges on the inside to help it snap into place, so it holds onto the bottom much better than the original caps that Sodastream provides. 

I recommend printing it in PETG to allow it to flex a little and snap into place. TPU would probably work as well, though it may not hold as firmly.