Surly track cogs are threaded the same as a BMX freewheel (1.37 x 24tpi right-hand threads). This means that they will fit on single-speed rear hubs, as well as BMX freewheel hubs, but this application is not recommended. Track cogs are meant to work on track hubs only. 415 hardened CroMoly steel. 1.37" x 24 tpi. Chain Compatibility: 6, 7, 8. Cassette Body Type: Threaded, Track.