I believe the model you are buying is an FXDX. The FX designation is for the Super Glide line or style that began in the early 70's. There was the FXE which was the first Super Glide and then the FXFB Super Glide Fat Bob came later.The D stands for the Dyna Glide frame/style. I can't honestly tell you what the last X stands for. It's possible the DMV has shortened FXDX to FDX just for streamlining purposes. Great bike I want one. Have fun, be careful
