Gridfinity Pen pot, holds 30 pens. Should hold most pens and thin sharpies. No need to print out the gridfinity base if you just need a pen holder, it sit's perfectly fine on a desk without it. 

I found 4 of the hex inserts work best for me, this allows the pens to be held upright and still have space for the clip. I designed them to be modular so print as many as you need. They just stack inside the pot (the support pins are quite fragile, but I found that's not a problem once they're in place and they're not exactly load bearing), so print them out and just slide them in, the fit is quite snug so they aren't going anywhere and if you lose a pin or two there should still be enough left to keep the gap.

Edit:

Forgot to add, if you want to know more about Gridfinity check out Zak Freedman on youtube or the gridfinity website