~~~ with even huge quantities here in the US that were brought back by troops after WWII.

I had this one for almost 30 years and got a bunch more years later.

I know that my typing was incorrect way back then and these days I type either 70 mm x 50 mm or 70 x 50 mm (always with a space between the number and mm)...

The (RE) is my code for RMA, who I got it from in the early-90's.

The same correct rule applies here in the US... though no uniformity exists that I know of, even amongst educators...