Stainless steel and this was never used. It was installed and then immediately removed due to the aesthetics of the engine bay. It has been sitting in the garage for a couple years and during that time the Uni Filter, allen wrench, and two screws were misplaced. I added a lightly used K&N filter, which is actually an option that DDM offers, that fits perfectly, so this is ready to run. These sell new at DDM Works for $249 and I'm selling this for $200. Buyer pays shipping in the USA