I installed the new cartridge in my very old MSR Waterworks filter and it worked perfectly. Parts of the old filter that are no longer needed with this new cartridge: paper filter in the bottom, o-ring at the top and metal mesh screen at the top, you can throw those away.Now for the really bad part. I went to take the cartridge out of the housing to let it dry after my test. I pushed on the bottom of the cartridge while holding it over the kitchen counter. The thing popped out all of a sudden, bounced off the counter and smashed to smithereens on the kitchen floor!!!! I literally had this thing out of the box for all of 10 minutes before it was trashed.I had to immediately go online to buy another one because I am going camping in 3 days and will depend on my filter. Big time bummed at the extra, extra expense. Good filter though...In case you are wondering what it looks like inside there is a ceramic outer layer with a charcoal layer inside. See photo.