Mine is a '64 Custom 500. I saw that too but don't really want to pay 30$ with postage for one nut...I can find it here, too but just need to know the size of it.Here's one if you haven't found one.
Front wheel cylinder retaining nut. This is for one nut. Also check out our reproduction lock washers that keep these nuts from backing off, availablehere.www.ebay.com