Time for another stationery factlet: Staedtler was the first European manufacturer of mechanical pencil leads.
Staedtler made lead holders and leads for the lead holders for a long time. Below is a page from their 1935 catalogue.
When thinner lead diameters were introduced Staedtler was the first European manufacturer of these thinner leads – the kind of leads I would refer to as mechanical pencil leads.
Staedtler’s catalogues from the 1960s don’t seem to show pictures of these leads, but the catalogue from 1970 does – and it shows a very familiar lead container.
The Mars lead container still has the same shape today, but the plastic is now transparent. The opening of this lead container has the perfect diameter for refilling Mars micro mechanical pencils as you can see in the old video from my 2015 neox blog post.
I would like to thank Eberhard Rüdel for his detective work regarding my mechanical lead questions.