[Closed] inner ring problem

Just bought a mixed set of rings from the classifieds here.

Big ring (trushift) fits fine but not middle ring - middle ring is a shimano & my cranks are raceface.

Middle ring wont fit on crank as the tabs below the holes are about 1mm too long. Am I missing something here? Don't really want to try dremelling the inside of the tabs down as I'm sure they are quite hard steel.
I'm not that au-fait with the niceties of chainring sizes & could do with some pointers, don't want to buy another wrong'un...

Thanks in advance