[brian_]

Grote has braided ground straps with crimped-on ring terminals - they apparently just gather up the braid into a bundle to use a common crimp terminal. They don't anything short enough, but their products illustrate one way that they could be built.

The logic in favour of a cable connection make sense, but at this length a heavy round cable would have almost no flexibility, which is presumably the reason for wanting a flat braided cable.

 

[brian_]

Fine stranded boat cable is pretty flexible.

So long as there is a curve in the connection between posts, I do not understand why "more flexibility" would be desirable?

Absolutely. But these straps are only 76 mm on centre, so the cable length with typical terminals is only about half that, and in the gauge of cable used for this that's almost a rigid bar, even in boat cable. I agree that a curve would be good, but it's hard to get a curve in that short distance.

Some people have used solid copper straps for this sort of application, but crimped a curve into the middle to allow some flex. There are even commercially available bus bar expansion joints, which use a stack of thin sheets (in aluminum or copper) for flexibility, welded to solid end bars.