Not sure if, when or where this has been covered on this forum but here's a little information about the plugs used in our FiSTs. Fords Part # 12405 cross references to BOTH the Ford Focus ST and Fiesta ST, however, Ford uses a sublet number (i.e. SP-525, SP-532 ect) for internal tracking (but the plugs are the same, physically.. same heat range, same thread). Also, Autolite cross references XP-5363 as the direct replacement for all applications that use Ford part # 12405 (SP-532 and SP-525 among others). Interestingly enough, my 2011 Mazdaspeed3 used a FoMoCo plug which cross references to Autolites XP-5364 (same plug as ours except one range hotter) and *I used* XP-5363 (same spark plug recommended for our car and the FoST) in my modified MS3 and they worked GREAT. I hope one day I will see an XP-5362 part number because that will be a colder plug for our car.