Probably a 1/4" cable....ill probably take some heat for this but right now im not running a safety anything...but man it looks nice....i will probably do a cable swap as well
Ummm No.

I have cables on all of our boat trailers. They work killer, but need to be DOT rated. I believe mine are all over 3/8" and have hooks with clasps.
The advantages of running cables are that they remove a major part of human error with the chains, plus they make no noise whatsoever.
An added benefit is that they stay snug, so there is little chance of them ever coming off accidentally.
GT