The OEM plastic fuel filter cap on your L5P Duramax is susceptible to rounding off when replacing the water separator and cracking during extreme cold weather conditions. Upgrade your OEM plastic fuel filter housing or FASS Drop-In Series with our Billet Fuel Filter Cap! The FASS Fuel Systems Billet Fuel Filter Cap was engineered and manufactured in the USA with the quality you’d expect from FASS. Our Billet L5P Duramax Fuel Filter Cap utilizes the same 36mm socket for removal and is equipped with a billet aluminum drain valve that allows for tool-free draining! The FASS Fuel Systems Billet Fuel Filter Cap was engineered and machined in the USA out of 6061 billet aluminum.