late 70s school pen cartridge question

[manoeuver]

A friend of mine was telling me about the pens she brought back to the US from Germany when she finished school there in 1980.

She's had trouble finding cartridges that will work in her pens. Can anyone here tell me if the pens made for the school Market in the late 70s in Germany used a proprietary cartridge?

If so, anyone know where I might find them? If not, which cartridges ought to work in my friend's pens?

Thanks all!

[Pterodactylus]

It would help to know which pen it is.

Most common where international (Pelikan) cartridges.
There were also Parker and Lamy cartridges.

Most likely one of these will fit.

As you posted it in the Pelikan forum we might can assume that it is a Pelikan pen, in that case every international cartridge will fit, Pelikan used nothing else.

Everything else than the 3 cartridge types above are not very likely (as would be considered as a very exotic thing at that time, assuming we are talking about West Germany).