Surly Track Cog - 1/8".
Fixed Gear pinion of Surly, for 1/8 "chains (track-Standart)
made of chromoly hardened
Fits on Formula, Dia-Compe Gran Compe-, Suzue inter alia hub
thread: ISO 1.375 "x 24 TPI
Surly says:
We choose ISO Threading (1,375" x 24 TPI), due to it ''s compatibility with other threads used on bicycle hubs.
ISO threads fit English and Italian threads almost perfectly.