Originally Posted by
jimmuller
dbakl's explanation is quite accurate, no further explanation necessary. Your original description was that "a bolt went through to a bolt on the back of the dropout", or something similar. What you meant was a bolt from the upper knuckle of the derailleur went through the dropout hole to a special nut that fits on the inside of the dropout.
This may be a matter of semantics, but I did indeed mean that a
bolt goes through the hole from the
inside of the dropout and threads directly into the back of the RD. There is nothing protuding from the back of the RD that goes through the dropout, it is flat with a threaded hole that accepts the
bolt I'm referring to.