A cracked fuel filter cap can lead to air in the fuel system. That can result in hard starting or potential fuel injector issues. A cracked fuel filter cap can also cause a fuel leak, which is definitely a bad idea on a hot engine. Never worry about that again with a Sinister Diesel Lower Fuel Filter Cap. Constructed from a single solid aluminum billet, the Sinister Diesel Lower Fuel Filter Cap is far stronger than the OEM plastic cap. It's anodized in Sinister Blue for corrosion resistance and features a 18th NPT port for testing fuel pressure. FeaturesImpervious to cracking like the OEM lower fuel filter cap, CNC Machined from solid aluminum billet, Features a 18th NPT port for fuel pressure testingIncludes(1) Sinister Diesel Lower Fuel Filter Cap, (1) O - Ring.