It's just a thumb shifter.
I'd guess it has to be the front-mech shifter (as it has no friction) or a rear one with the friction removed somehow.
@turnpedal started
London Fixed Gear and Single-Speed is a community of predominantly fixed gear and single-speed cyclists in and around London, UK.
This site is supported almost exclusively by donations. Please consider donating a small amount regularly.
It's just a thumb shifter.
I'd guess it has to be the front-mech shifter (as it has no friction) or a rear one with the friction removed somehow.