Before anyone yells, I searched and could not find any definite answer to my question, though I am sure it has been asked before. I am in the process of converting an old hybrid beater to a single speed, and need to know if a simple single speed cog will work, or if I need a freewheel. I want the bike to coast, not looking for a fixie. Does a fixed cog coast depending on the type of hub, or is a fixed cog always for a fixie?

Can I just use this:


Or do I need one of these?:


Here is a picture of the bike if it helps.



THANKS!!