Why can't a get my hose to screw onto my spigot and not leak?

I've tried 3 different hoses and new washers, but no matter what I do I can't tighten the hose enough to make it not leak when I turn the water on. The spigot isn;t what's leaking, its from where the hose connects to the spigot. It's alomost like the threads are different so I can only screw it on a little bit but not enough to tighten against the washer and get the seal. Do they make different threads? Or is my spigot just old and corroded so much that the new hoses can't screw onto it well?