Originally Posted by
Bill Kapaun
It sounds like a Uniglide-
https://www.sheldonbrown.com/k7.html#uniglide
Assuming you have the screw on smallest cog- you may be able to find a smaller one on ebay etc.
Do you plan on changing your next smallest cog too, or living with a noticeably wider jump between 5 & 6?
You still haven't said what the largest cog is in the back. that can also make a difference regarding "how small" you want to go.
You have to plan your progression of cogs. If you were to go to a 12T (IF you can find one) you may have to change the 2nd cog (if you can find it)......
Thanks for that link Bill, it really cleared up my issue. I'm posting the pics in the next box for everyone to see, but it appears to me it's a hyperglide from the late 80's.