HAH! I had to take my stupid muffler off my car. its the stock one with 225,000km on the engine.. I'm too poor to put a new one on it atm since I've had to replace the coil AND ignitor in my distributor (almost $300), but when I was lookin for what size.. to my surprise 12mm for the damn exhaust bolts. At least they made it simple enough .. 10, 12, and 14mm is easy to find.