It DEPENDS ON THE THREAD!!! Sorry to shout, but you might quilt with super fine silk and a 70 needle, or thick thread and a 100. The Superior Threads site has excellent, thorough info on this. Using a needle that's too small for your thread will cause shreds and breaks, too big and you are putting big holes in your fabric for no reason. It's like asking, "what size pants should I buy?". It's going to depend on what you are trying to squeeze in there :).