Vintage RPF 6 espresso porcelain coffee cup set

Vintage RPF 6 plan porcelain espresso cup set up to transparency. Most likely purchased in the 1970s or 1980s in the so-called Handy Hands store, where defective and non-standard items were sold. Without factory logo on the bottom. No defects, but not perfect, especially the shape of the saucers, which can be seen when stacked.