15t, 3/32. Machined generic brand.

Has about 3500 miles on it, mostly with either a 40t or a 42t ring. I just put on a new chain, and when I went for a ride, it would make this rattle sound from the rear - as if I had a derailleur - when accellerated. The chain was tight and as far as I know, the chainline on this bike is pretty good.