Amazon.com : ENBO Shimano Bike Rear Derailleur RD-TY300 6/7 Speed Rear Derailleur Road MTB Bike Mountain Bike Direct Mount : Sports & Outdoors
My daughter's Trek came with a 6-speed Shimano Revoshift SIS Index. It's a new bike. She can shift to higher gears easily but does not have the grip strength to shift back