how high end do you wish to go? if your aim is to simply set up a 7spd index is should be aesy to find a RD with a 'claw' attached.
here is just the hanger 'claw'
http://www.loosescrews.com/index.cgi...d=213993527782
here is a Tourney with a hanger attached
http://www.loosescrews.com/index.cgi...d=213993527782
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“One morning you wake up, the girl is gone, the bikes are gone, all that's left behind is a pair of old tires and a tube of tubular glue, all squeezed out"
Sugar "Kane" Kowalczyk