Sorry Tim, I don't know the internal details. They started as a 35th anniversary model (35 only) and I recall that they made them for another year, but they never really caught on. It is interesting to play. Bass lines are clean without octaves, but the treble strings sound like a 12-er. An unusual combination..... but I've heard "10 strings" before with the two bass octaves removed, and they are quite similar.