And straps on the rest.
That was the general rule when I was driving flatbeds for Arrow.
The idea is that chains will be strong enough to keep your load where it belongs.
You also use chains on wire spools because of the weight.
The general idea of strapping and chaining is that you make the load part of the trailer. That way if something bad does happen, it won't spill all over the highway and innocent four wheelers.
This is what I noticed when I got to the Wally-world parking lot this morning.
And as I was leaving...
You notice that he's only got five straps on that almost 48 feet of square steel tubing, didn't you?
When you see something like that, you really should think about getting ahead of him or what you'll do if that load ends up on the road.