This fuel cap was designed specifically to fit the 6.6L Duramax Diesel Trucks and threads right into the factory filler neck. It is constructed of T6 6061 Aluminum and is anodized in green for corrosion resistance and to give you that extra reminder to fill up with Diesel fuel. We designed this cap with a set of magnets to the cap so you don't have to worry about losing your fuel cap off your bed rail after forgetting it when filling up your Duramax Truck. This cap if perfect for Duramax owners that want to keep their diesel in their tanks, while also looking good. Deter thieves and keep your fuel clean with this locking fuel cap. We designed this with flatbed and service bed owners in mind, when your fuel cap is out in the open 24/7 and shining in the sun, it may attract some extra attention, now you wont have to worry about anybody stealing your fuel cap with this secure locking design!