There are two types of cartridges line, those with a quick coupling fitted to each end, and also those with a pitch of 1/4 inch.
Each cartridge filter specifically water, depending on what it renforme.
They have a inscrisption "FLOW" with an arrow. This determines the direction of flow of the water during filtration. So, on the side of this entry, it will output to a new cartridge or to the faucet installed on your sink.