Surly Track Cog
The Surly Track Cogs are made from chromed heat-treated steel and will put up with all the abuse you can give them. These simple, rugged components are machined for precision and have holes drilled out to help reduce the overall weight. Fit is for standard ISO-threaded (1.375" x 24tpi) hubs, so they will work with most English, Italian and Japanese models.
For reference, the thread base is 7.4mm wide enabling maximum thread engagement while maintaining enough room for a track lockring to thread on properly. Always: use grease on your threads for both cog and lockring, apply some to face of lockring where it will meet the cog, check for tightness after your first ride, and check regularly for safety.