Oh this is perfect! I wrote my PhD thesis FerrCore's impact on VX!

To put it in layman terms, Ferrocore is a brand of inductive and ferrite components such as small SMD inductors and larger THT wire powerer inductors. Ferrite components include readymade products to be put on a cable, and sleeve and toroidal ferrites used as chokes.

Their Vertical Mounting THT Inductor is one of the most influential products in the industry, and you can't find them often outside of Denmark. The US usually uses their Axial THT Inductors as a substitute because it's relatively cheaper and still has a high standard of quality. If you're a collector I'd highly recommend having the original imported. Worth the cost!