The screw is 10-24; that fits easily through the chain's links. A #10 SAE flat washer goes under the screw's head and under the nut. The nut is a nylock self-locking nut. (1/4"-20 just fits through the chain's links as well, but the fit is too snug, and it will jam when you begin to tighten it. M6 might work, but I don't have any M6 screws that are long enough.) There's more chain there than I'll need; I'll just lop off the extra when I've got the installation partly done.
Installation on my '99 Ford Ranger was easy. The hanger affair above the muffler that's attached to the underside of the box gave me a secure place to drape the chain over. Then, it was just a matter of getting the 2" long screw in place and the nut started on it. At that point, I lopped off the extra chain with a bolt cutter. I tightened the screw just to the point where the chain was beginning to take the load off the other hangers in the system, and I was done. Here's how it looks on the truck.
I'll check the chain's tension in a week, tweak it if need be, and that'll be a long-lasting, trouble-free repair.
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