The slit of nib looks to be at a slight angle. I put a few drops of Qwink in the old cartridge for testing. Looks wider than medium but it may just be that the ink is watery. The item "Rotring 600 Fountain Pen Black" is in sale since Tuesday, January 14, 2020.
This item is in the category "Collectibles\Pens & Writing Instruments\Pens\Fountain Pens\Rotring". The seller is "terry5732" and is located in Minneapolis, Minnesota.This item can be shipped worldwide.