Last week I was on a night ride and something unseen (a stick I suspect) grabbed my rear mech and ripped it off - busted the replaceable hanger on my Cannondale Rush. **** happens. Next morning in the light of day I went over the derailleur to see if it was bent - it looked OK structurally apart from some small scrapes. To my annoyance I noticed however that the low limit screw had been ripped clean out, plastic insert and all (spoke got it, I assume). Further to that, the hanger bolt was missing its flange.

To my way of thinking, the flange on the hanger bolt looks like it's only held onto the shaft by a hair's thickness of metal, And reading around, it seems the limit screws and their plastic inserts give trouble from time to time as well.

I love SRAM and have had X9 on my last three bikes, but it seems like these two areas let the rear mech down a bit - particularly that hanger bolt, where a few grams more metal at the flange would make it a whole lot stronger.