79pmooney

There are several companies making 12t cog and lockrings. Eurasia has them. Be aware that if you ride Miche hubs, it is going to get expensive because the available 12t lockrings are for standard (lefthand) threading and the Miche threading is different (and fortunately, slightly bigger diameter). A machinist can re-tap to the Miche standard, but if he is smart, it will be expensive! Those lockrings are very hard. He may have to stop and resharpen his tooling several times to tap, what, a 1/4"?

I've been this route, not for the velodrome but because I had a custom fix gear road bike made to ride serious hills. Since I have to go up, it is a given I ride a 42t chainring. A 12t gives me 95" for the descent. Not huge coming off Crater Lake or down the famous descent into Ashland, OR. That lockring, $/gram is like expensive jewelry.

Edit: The 12t lockrings are bell shaped, looking from the rear. Narrow at the cog and extending out about an 1/8" before flaring out to the normal lockring diameter so a standard tool can be used. Hint: The Park lockring wrenches suck here because they are narrow and tend to slip off to the inside if you don't pay attention. The Pedros Trixie fix gear wrenches for the hip crowd work far better. They are thick enough that you can hold the wrench against the cog just like you normally would. I carry the Trixie under my toolbag, but it gets used every time at home when it's the 12t lockring.

Ben