The FS1232 uses the factory screw in drain, the FS1221 has the drain with a plastic knob you turn to drain. They both have M16X1.5-6H threads the FS1221 is about 2.5 inches longer. There as about 20 fuel/water separator filters that have the same threads anywhere from 3.32 long to 8.61 long.
A forum community dedicated to Dodge Cummins Diesel truck owners and enthusiasts. Come join the discussion about reviews, drivetrain swaps, turbos, modifications, classifieds, builds, troubleshooting, maintenance, and more!