This is untested and not suggested for use! I have been looking at designing a refillable replacement for the extend air cartridges used by the O2ptima rebreather Improvements to be made... Add an indent or similar for a max fill line find a tube to use rather than all thread so that the factory oxygen tube can still fit through the middle. Gas deflection widget to prolong breakthrough at the top of the cartridge. I have added a second version of the cap please see instructions I have redesigned this and put the pictures up of the first prototype i have used parts of a Poseidon cartridge for the mesh on the bottom. the cut-out guide has two holes to aid in marking a circle to cut out mesh for the body and for the cap. an alternative would be to make a solid disk the right size and then print it with no top or bottom layers and adjust the infill shape and percentage until you got a good mesh. the rod is M5 stainless all thread Cap v2 after thinking about it it seems silly to have to make an entire new housing when there is already a perfectly good one with the unit. simply print two of the cap v2. fit threaded rod to one of them with a bolt either side of the cap. insert assembly in the housing from the unit with 1 end cap installed, fill with scrubber and the put the other cap v2 on and bolt down and install the other end cap of the unit. it would be worth using something like an open cell foam so if the scrubber settles during the dive it can take up the slack. pictures soon