RobertN - Good points. I used a shackle (clevis, shackle, whatever) on the drawbar for years. Lately I've taken to using a grab link because, even if the chain loosens, the tractor can't slide sideways (more than the slack in the chain anyway. It's a fine point, and probably not worth worrying about, but if you're obsessive, you might want to. /w3tcompact/icons/wink.gif
Also, here's something else I've seen a lot of people make a big mistake on: hooking the chains to the trailer. If you hook them to the bottom of something, and the chain loosens, it'll fall completely off. If you wrap it around or run it through, drop the hook down from on top, gravity will hold it there, even if the chain loosens, and the tractor can never move more than the slack will allow.
Mark