They worked for my use, they'll probably work for yours.
I'm definitely not using them for their intended purpose, but they work great.  I write with fountain pens, and refill my own cartridges.  These plug the end nicely.  I'm extra paranoid, and put the cartridges in a case to prevent leaks, and that's in a baggie, but these haven't leaked at all (and the ink I use is deliberately incredibly good at creeping).  It would have been smarter to get the specific size, but I wasn't sure what size.  The documented sizes are 100% exactly correct.
Rating: 5 stars