Somehow in the upgrade fever I had recently, I ended up with 3 Rival mid cage derailluers and a force mid cage derailluer for Contador. I put one on the gravel bike. And another will go one the zwifting rig. And apparently I will have a spare? Still waiting on the shifter for the zwifter, then that will get upgraded to 11 speed. Can't do the gravel bike, cassette won't fit so that will stay 10 speed.