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
SHIMANO REVOSHIFT Shifter SIS INDEX 6-speed | SHIMANO BIKE-EU
Shimano Tourney SL-RS35 Revo Shift Lever Bike Bicycle Speed Shifter L+R | eBay
Bicycle Bike Shifting Lever | Shimano Shifters Revoshift | Bicycle Shimano Revoshift - Bicycle Derailleur - Aliexpress
Shimano Nexus C6000 Revo Shifter - Living 360 Bike Shop | Boerne, TX
REVOSHIFT SHIFTER | SHIMANO BIKE COMPONENT
Amazon.com: ZUKKA Revoshift 6 Speed Shimano Right Shift Lever SL-RS35-6R Bicycle Twist Shifter Lever Mountain Bike Commuter Bike Folding Bike : Sports & Outdoors
Amazon.com: ZUKKA Revoshift 6 Speed Shimano Right Shift Lever SL-RS35-6R Bicycle Twist Shifter Lever Mountain Bike Commuter Bike Folding Bike : Sports & Outdoors
How To Replace Shifter Cable On Shimano Revoshift Shifters - YouTube