Virtually all chains are more than strong to use on a propoerly aligned single speed or fixie. In the early 80's, some top level track riders used Dura Ace 10 chains, which were smaller and much weaker than any chain commonly used on bicycles today. The only problem is connecting them as strongly as the rest of the chain is made. Super narrow 9s chains are only as strong as whatever joining system is used. For single speeds I use inexpensive KMC chains. The KMC website gives dimensions and specs dfor all their chains. I just pick the one with the longest pins, which results in more extention past the sideplates and an easier chain to join.