If your faucet has two handles, you have either a compression type or a cartridge type. How do you tell? Compression (or stem type) faucets have been around for ages. Cartridge types are a relatively recent phenomenon. If you don't have the installation instructions that came with the original faucet (fat chance, right?), you're going to have to put on your plumber's hat and do a little hands-on research. Start by shutting off the water supply and removing a faucet handle. Most all handles are fixed on with a screw, which you can usually find under a decorative cap that you pop off with a small screwdriver. Remove the screw, then lift or jiggle the handle off. (Warning: This is not always as easy as it sounds.) If you see a shaft going down into the body of the faucet, you have a compression type. On the other hand, if you see the innards encased in a plastic body that you can lift out easily, you've got yourself a cartridge type.