We use chains on the farm. I think our big chain we use for pulling and lifting is 1/2 inch grade 70. I think the most dangerous thing you can do is jerk on stuff. That's when things usually break. If it don't move get a bigger tow vehicle. For heavy stuff like tractors in mud another option is to use two tractors to pull it out. Hook two seperate chains/straps to the stuck machine and pull away from each other at a 30 degree angle or so. Creates a bow effect and the stuck vehicle should move. And if your really screwed
you can dig you around and pull. They also can lift the vehicle up and over a bump. And while their are their they can dig a tile in and fix the ones you broke.
Jamie