What are your front chainring sizes?
Ensure you know the difference between a cassette and a freewheel and which you have. For a 2x6 you're very likely to have a freewheel and freewheels don't often have smaller cogs than 13 or 14. If you've got a 6 speed uniglide freehub then your cassette options will be limited.
Last edited by Narhay; 04-27-22 at 07:35 PM.