I have a pair of 505s and IMO they have the same fit as 501s. They strike me as 501s with a zipper fly, as previously posted. You can find one vendor who confirms this, here:
http://www.sheplers.com/item.cfm?DI=...RT=2&show=page
http://www.sheplers.com/item.cfm?DI=...RT=2&show=page



