SP Tools’ 24mm flare nut wrench, No. 66150, is designed to slide back into the recessed area of the cylinder head, where the fuel line retainer screws into the head. The special depth and angles flare nut wrench lets users hold the 24mm retainer in place while they loosen the 19mm coupler to the high-pressure fuel lines. This tool is designed for the Cummins common fuel rail set up on the 5.9L motors 2003 and later, and 6.7L 2007 and later. Cummins 5.9L & 6.7L diesel motors can be found in Dodge trucks starting in 2003 and other trucks using the Cummins 5.9L and 6.7L motors with a common fuel rail.