Murray--

Clawhammer, sometimes called Frailing or Rapping the banjo, is the traditional style that was predominant, at least in most of the Appalachian U.S. south, prior to WWII. You can hear/see examples of the style on albums/videos of Grandpa Jones, of of most old-time Appalachian string bands.

Banjo makers at one time did make the 5-strings in different sizes, but I suppose current ones are mostly of a uniform construction. A friend of mine has an old "piccolo banjo," which is favored by backpackers in my part of the country, and which must be tuned in C.

Clawhammer banjoists quite frequently re-tune the banjo to play in different keys. Because many banjos were originally home-made, many of them were without frets, and there are still a few luthiers selling them at folk festivals and such places. The fretless ones are fine for solo work, but they don't make you particular with other musicians when you work with a group. More later.

Bill