New Shimano SIS RD TY15 Rear Derailleur 5-6-7 Speed - NOS | eBay
Replacement for an old 6-speed SIS rear derailleur : r/bikewrench
SHIMANO TOURNEY Medium Cage Rear Derailleur 6-speed | SHIMANO BIKE-EU
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