An update here!
Just measured the lug size of my Black & Orange Rule ( 馃榾 ) and it is 21.5mm. I measured also the Black Nato Strap ( Black with Orange Borders ) and it is indeed 21.5mm, which makes a fit and exact match to the Watch.
With regards to 19mm Nato, The one at the OB could be a manufacture Error to have it exact 19mm....Will keep searching and update!
Regards