This particular header system will fit all years Elantra from 2001-2006, and either the four door sedan, or five door hatchback. As with all of our header systems, we only use the highest quality stainless steel at our Korean factory where these are produced. It is all mandrel bent, and has beautiful welds. Worried about the noise? Our header systems are all developed so that they do not sound like the typical "bumble bee" buzz that annoys most people. Both O2 sensor holes are included for easy install, one on the manifold, the other on the flexpipe (long). We have 2 flex pipes available. One is the long flex pipe that attachs all the way to the cat back exhaust piping. If you want to install a high flow cat into the flex pipe, there is a long straight section of the pipe you can cut for this. The other option is for the short pipe, which you can use so that you can still attach your stock cat to it (welding might be necessary). Installation is very easy for any exhaust shop, or even someone mechanically inclined, as there is no cutting or welding needed to install.