Originally Posted by T-Mar

The Z-series are very non-descript from the front, but if you look on the back of the parts, there will be part numbers, format XX-YYYY-ZZ. The XX prefix indicates the part type (i.e. FD = front derailleur, RD = rerar derailleur, BR = brake, etc.). The YYYY body is the series and part number identifier. For the Z series it will start with Z, followed by three numbers. The ZZ suffix is optional and used to designate component options (i.e GS= large capacity derailleurs). Examples of Z-series parts would be RD-Z503-GS, FD-Z202, BR-Z306. The key is the Z at the start of the series identifier. I trust this helps.