An awful lot about bicycles can be determined by simple inspection. If you look at the pulleys on a modern derailleur, you will see that they are marked very differently. One may have a directional arrow on it, and the other may be marked specifically for 10s or 9s. These differences alone would suggest that they cannot be swapped. A simple wiggle will also show you that the top pulley can slide from side to side (what Shimano used to call Centertron, or something like that) while the bottom one does not move.MPH74 said:Are the two pulleys on a Shimano Dura Ace 9 speed rear derailleur interchangable (i.e., are they exactly the same)? Are they generally interchangable on other rear derailleurs?