You gentlemen surprise me. And make me actually go and measure. And get 19.64mm. In any case, all of my angled tonneaus ride quite happily on 19mm straps.
Yeah, now that I'm home with the micrometer, I'm getting 19.55mm. But I round up... I like my bands snug with no wiggle room for spring bar shenanigans.
Excellent. Approximated and not strangulated. It doesn't exude the devil-may-care insouciance of LouS's 19mm bands, always flashing a dangerous glint of spring bar, but it looks like it will serve quite well.