The Tiny Hole in a Fountain Pen Keeps It From Cracking
The slit feeds ink to the paper, and the small hole keeps the split from cracking further.
The Rest Is Science · The Fluid Dynamics of Fountain PensLook closely at the tip of a fountain pen and you will see a thin slit running up the metal, ending in a tiny round hole. That hole is not decoration, and it is not where the ink comes from. It is there to keep the pen from breaking.
The slit is the pen's plumbing. Ink travels down that narrow channel to the tip, where the ink meets the paper. The metal around it has a sharp cut in it, and that end point is a weak spot. Left alone, that line would crack further, leaving the split physically weaker.
The hole solves that by giving the stress somewhere to go. Hannah Fry, the expert, put it simply: drilling a small opening at the end of a crack spreads out the forces so it does not crack further.
It is the same repair used on aircraft. If a crack appears in a fuselage, engineers drill a small hole at the tip of the crack to spread out the forces so it does not crack further.
Counterintuitively, then, the slit is made stronger by removing metal. Without that hole, the split would keep cracking further.
Questions people ask
Why doesn't gravity just pull the ink out of the pen?
Ink moves mainly by capillary action, the tendency of liquid to creep through narrow spaces. Gravity alone is not in charge. That is why the pen does not simply drip when pointed down.
Do engineers have a name for this trick?
Engineers often call it a stop-drill or crack-arrest hole. The idea is the same in metal, plastic, or glass: replace a sharp crack tip, where stress concentrates, with a blunt round hole that distributes it.
Does the hole control how much ink comes out?
Not directly. The slit and hole help deliver ink, but too much ink would flood the page. That job falls to a separate part under the nib called the feed, with tiny channels that hold extra ink back.