One of our colleagues was recently in South Africa, where he has measured common foundation, which is sold in a country store.
Here are pictures of the foundation from southern Africa, near Hermanus. From a country store which just sells frames, hives, clothes and honey, but it is not specifically for beekeepers.
I have measured (outer cell wall 1 to inner cell wall 10):
4,65mm / 4,65mm / 4,85mm
(These are the measurements in 3 different directions of the hexagonal cells)
This is far less than the 4.9mm and you remember that the usual cell size in Europe is 5,4mm!
And it is said that the Cape honey bee has now no more problems with Varroa mites!
click to enlarge