There are plenty of ball point or roller-ball refills which come with a plastic cap over the tip. Most roller-balls will dry out if not sealed, so I would suggest you get a regular ball point refill anyway. And they don't have to be sealed. Consider some of the tiny refills: I have the ultra small Fisher refill. Smaller than the pencil in the Ritter PSC. But in actuality I think the pencil is more worthy of the space than the pen refill.