Buy a proper SS cog. The pirated cog from a cassette will be likely to derail at the worst possible time, like when your hammering up a muddy hill.

They're like $5.

Like this:

http://www.webcyclery.com/product.ph...cat=402&page=1

More:

http://www.webcyclery.com/home.php?cat=402


DON'T get alloy chainring bolts.