To the inexperienced all chains can look very similar. In reality it can be quite tricky to get the answer to this question. Try looking at http://www.oregonchain.co.uk/ for some help. You can view a comprehensive guide to chainsaw chain at http://www.oregonchain.co.uk/pdfs/MaintManual_English.pdf
This contains everything you're ever likely to need.
Happy cutting!
Andy, October 2008