Fun fact: Merkur was used to build world first machine for casting soft contact lenses :)

It's a great story. Picture here: https://en.wikipedia.org/wiki/Otto_Wichterle

By late 1961 Wichterle succeeded in producing the first four hydrogel contact lenses on a home-made apparatus built using a children's building kit (Merkur), a bicycle dynamo belonging to one of his sons, and a bell transformer. Wichterle also made all the moulds and glass tubing needed to dose them with monomer. On Christmas afternoon, with the help of his wife Linda, using the machine on his kitchen table, Wichterle finally succeeded. He tried the lenses in his own eyes and although they were the wrong power they were comfortable. Thus, he invented a new way of manufacturing the lenses using a centrifugal casting procedure. A few days later, he completed his patent application and produced over 100 lenses by spin casting. He built several new prototype machines using Merkur toys with increasing numbers of spindles which required the stronger motor taken from his gramophone. With these rudimentary devices, in the first four months of 1962, Wichterle and Linda made 5,500 lenses.

I used my old set recently when I quickly had to hack construction for grow-lamps.