10/4 on Russ's advice.
The aerosol cans of spar varnish are pretty good products, we use them at work on the occasion to spray that one item that was missed when the rest of the bookcases/trim were varnished. I've also used it on mitered-corner boxes and such.
GIVE IT A TRY on pens. The biggest downside to spar is the curing time. Overnight is best before you try to assemble the pens. And don't spray the coats heavy or they drip..... and don't spray too many coats or the finish might chip as it ages. Spar is a very durable product, just has a few user-unfriendly characteristics.
If you get dust in the spar as it cures, buy yourself some Micromesh sanding pads (1500 to 12,000 mesh) and sand the blank smooth, using the highest levels of micromesh to buff the pen to a high gloss. Let the pen blanks cure out for a few days before you micromesh.
As a side note, Russ's CA/BLO finish, followed step by step as he outlines it, will give you the FASTEST durable finish you are going to get on a pen. There are variations of this finish out there, though. Nail Russ's method down and then experiment.
