A thumb-operated derailleur
"I bought this as part of a complete drivetrain upgrade, and since I'm used to Shimano shifters, I was surprised that shifting up and down is done solely with the thumb—but I found it easy to get used to. Shifting in groups of four is convenient, but since my thumb is small, it’s a bit of a stretch, and I had to install the shifter almost horizontally given my high riding position on the mountain bike."
