Shift Ball Jam Nut 12mm x 1.25 Thread for 2005-2014 Mustangs.
Use this to tighten your CJ Pony Parts shift knob to the shift lever. Without a jam nut, your shift ball may not be aligned straight when the knob is tightened onto the lever.
You may also consider upgrading to a shift boot retainer which will also function as a jam nut while eliminating the gap between your shift knob and shift boot.