I have a flip-flop hub that came stock on a Trek single-speed. I'd like to install a fixed-gear cog and lockring opposite the existing freewheel. How can I determine which cogs and lockrings are compatible?
I've read Sheldon's explanation. I've also read this SE question. I understand that ISO (1.375" diameter x 24 threads per inch) is the most common. But I'm not quite ready to assume that my hub is ISO-threaded. State Bicycle, for example, says that their hubs are British-threaded. And in my experience, Trek's part selections can be quirky. Unfortunately, Trek offers no reliable way to look up the part specs for a given bike.
Opinions seem to vary about which if any combinations of disparate thread standards are a "good enough" fit. Some say you should never mix and match. Others say British and ISO are compatible despite their differences. I don't know enough to form my own opinion.
I'm also confused about how the lockring threading relates to the cog threading. I understand that the cog and lockring threads are different sizes. But I haven't found any information about lockring thread standards.
So, I think my question boils down to three sub-questions:
- How can I determine my hub's thread standard? (I think calipers are the answer, but confirmation would be appreciated.)
- Assuming I have either an ISO- or British-threaded hub, are the two indeed compatible?
- Once I know what kind of cog I'm buying, how do I select a compatible lockring? Do I need to take another measurement?