It’s been awhile since I’ve used cartriges (I like nice messy ink bottles...), but usually, you open the pen up, drop the cartridge into the bottom part (i.e. the part without the nib) with the skinnier side of the cartridge pointing up toward the nib, and then screw the nib unit back on gently until the cartridge kinda pops - a little hole gets poked into it. It looks like the metal ball is on the opposite side, so it’d go down toward the end of the pen.
Does any of that make sense?
Well, I kept trying and trying to push the skinny end of the cartridge down onto the spike (which is sheathed in a plastic tube) and couldn’t so I turned it around to where the metal ball was hitting the spike and popped it right on. It made a bit of a mess on the little grey grill like thing, but didn’t leak and writes great!
I’m thinking cartriges for Matthew, for the time being...we’ll do the converter thing eventually.