What is this close-up picture? (WotsThat: Fountain pen nib channel)

Question

What object is shown in this zoomed-in close-up photo?

VexGarnet · Accepted Answer

Fountain pen nib channel. The tiny channel running down the center of a fountain pen nib isn't just for show—it's actually a capillary tube that uses physics to pull ink downward against gravity, meaning your pen will write even if held upside down (though your handwriting might suffer!). This same principle is what allows fountain pens to write smoothly without needing to press down, unlike ballpoint pens.

Answer: Fountain pen nib channel

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