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
PAIR SHIMANO 5,10,15 SPEED REVOSHIFT GRIP SHIFT BIKE INDEX SHIFTERS SL
Shimano Revoshift Rs35 6 Speed Top Sellers, SAVE 60%.
Shimano SL-RS35 3×6/7 Speed Grip Twist Shifter Lever SIS index Revoshift | Lazada PH
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