This brass adapter will allow you to use a 400g Soda Stream bottle with this mini regulator. 

The adapter  screws into the 16gm port on the regulator

400gm soda stream canisters are more cost effective than 16gm cartridges but still portable enought to carry.  Also small enough to fit in the fridge if you are force carbonating.

THIS ADAPTER PRESSES THE GAS RELEASE VALVE ON THE SODA STREAM BOTTLE.

MAKE SURE YOU PUT THE ADAPTER INTO THE REGULATOR THEN SCREW IN THE SODA STREAM BOTTLE.