So I went to the hardware store today and got a few o-rings in case I want to turn one of my Sheaffer school pens into an eyedropper-filler.

No harm done if I change my mind and want it back as a cart-filler, right? Right?

Anybody have experience in this matter?

*silicone grease is not for me*

I was thinking about something like a tube that can be filled with a eyedropper. What are o'-rings?

O rings are round rubber gaskets... as opposed to rubber washers which are flattened.

I've had no luck with o-rings. Silicone grease is the only way to ensure a good seal. The o-ring would have to compress in all the right directions to make the seal airtight so the exact o-ring size is essential.

My one eyedropper pen---the Recife---has an o-ring. I figured if it worked for that one it might work for others. But I can see how an exact fit would really, really matter.

Thanks. It's worth a try or waste of time.