I have one of these https://www.sjscycles.co.uk/gear-shifters/sunrace-m90-friction-thumbshifter-left-hand/
As supplied to me by @maynardeames
I've yet to fit it. Or start the conversion. I'm such a slacker.
Also, as I understand it, if you have access to a Dremel (other die grinders are available) it's possible covert a 2 speed shifter, into a 3 speed, by giving it an extra notch.
I have one of these
https://www.sjscycles.co.uk/gear-shifters/sunrace-m90-friction-thumbshifter-left-hand/
As supplied to me by @maynardeames
I've yet to fit it. Or start the conversion. I'm such a slacker.
Also, as I understand it, if you have access to a Dremel (other die grinders are available) it's possible covert a 2 speed shifter, into a 3 speed, by giving it an extra notch.