I wanted to replace the output hose for my Katadyn pocket water filter with a longer hose, and after several attempts ordering the wrong size, I found that the right size is 3/16" I.D., 5/16" O.D. (and 1/16" Wall). It's not exactly the same as the Katadyn hose- the inner diameter is larger, and the wall is thinner (see the photos I uploaded), but it works. The metal clip fits around the outside, and the hose fits tightly around the output nipple of the filter. I'm only using this for output, so I can't say for sure if it would work for the input hose (where a tight seal is critical to maintain vacuum), but I think it would.