Available for: 2010 - 2019 Cummins ISX12, ISX15, X12, X15 Engines Performance Diesel’s BIG BOSS Oil Fill Caps are CNC machined from high-grade billet aluminum for longevity and superior performance. OEM fill caps are made from inferior plastic which is known to fail and leak oil. Due to vibration and inferior engineering, low-quality oil fill caps have been known to come loose and fall off while driving down the road. Don’t get caught in a bind! PDI Oil Fill Caps are structurally superior with a lock-tight design which has been field tested for strength and security.