Instead of a crescent wrench which can slip and damage the nut go out and buy a good "combination" wrench
http://buy1.snapon.com/catalog/item....e=snapon-store of the proper size for your nut. SAE & Metric are available. Get it at your local auto parts or Sears cheaper than this though. Good leverage and NO slippage. Get a "6-point" if you can find it.