Originally Posted by astrodaimler
That's the "stopper" to keep the deraileur from spinning towards the chain stay. Try
www.loosecrews.com. Before those tabs, there was a piece that you put in between the dropout and the derraileur and it creates that "tab" that you see.
Didn't see anything like that under "rear derailleurs Miscellaneous" on Loose Screws. Would this be something that would fasten onto the place where the tab used to be? There is the part still there the chrome part that's visible in the picture, that has a tab which is supposed to butt against that raised part that's been ground off. The hole that's visible may have some vestiges of threads in it, I can't tell for sure.