I found a dumpster Schwinn that I am restoring. This is my first time doing such a project. The bicycle originally had a 7 speed rear cassette. I want to convert the bicycle to single speed. I've removed the rear cassette to expose the free hub. What next? Do I buy a single cog, install spacers and tighten the lock ring? I don't want to talk about gear ratios. I need some education on how a single speed conversion works. My free hub has 9 splines (one that is very thin unlike the others). Do I need to take measurements to make sure the cog will fit? What determines the size of the spacers?

Best,
blaubner