Originally Posted by Roll-Monroe-Co

http://www.bunchobikes.com/auto.htm

For the Bendix version, the two-speed hubs are substantially larger than the regular coaster brake hubs.

I think there were two of the two-speed models: red and yellow. One has ratios for a smaller wheel (yellow, I think). In the US, anyway, the two-speed hubs are somewhat rare (that is, you'll see a very large number of bendix coaster brake hubs for every one two-speed that you come across).

Fichtel und Sachs also made a two-speed hub (I believe these are regarded as superior).

Edit: Ah, better info here: http://www.trfindley.com/pgbndxhbs.html