Yeah, the spindle thats on the mustang. Since you cant grind down the spindle and the rotor, you just have to use spacers. But actually, at least for 99 Cobras, it IS the rotor. The rotor wont even fit all the way unto the rim because of the lip for the center cap of the rim. There was no choice for me, I had to install spacers and longer studs for me to install 99's. Even if I didnt care about the dust cap sticking out and having no center cap, I still couldnt fit the rim onto the rotor. I dont know if Bullitts are the same way, but sarcasm is not appreciated when you are wrong.