These came on my Specialized Crux. I caught a stick in my derailleur on a trail and it damaged the pulley.  I was used to the Shimano shifting and decided that this was the time to switch back over to Shimano. I'm including the derailleur for parts. I have seen replacement pulleys for sale but seems the price seemed expensive compared to the price of a new/used derailleur. No rash on the derailleur. Maybe you could use it someday.