Here’s Why Fountain Pens Have Fins

We don’t always appreciate the sophistication of fountain pen design as we write happily away. Fountain pens have a serrated, usually black, plastic or ebonite, outcrop directly beneath the nib featuring tiny grooves. These are called fins, and many older pens don’t have them.

The fins on the feed act as an ink buffer, preventing too much of it from flowing onto the page all at once. Ink spreads out along the grooves between the fins before moving into the nib. As you write, they empty, causing air to flow back into the cartridge and more ink to draw down into the feed.

Also called the comb feed, fins are small thin pieces of ribbing on the ink feed of a fountain pen that assist the capillary action by which the ink flows to the nib. If the ink cartridge isn’t full, the air in the cartridge expands from the warmth of your hand, pushing ink out and into the feed. Sometimes the fins aren’t visible because they sit inside the grip section of the pen.

The Feed System Of A Fountain Pen

A surprising amount of engineering goes into the making of a fountain pen.

The fins in the feed increase the surface area along which ink flows as it travels to the nib. The feed plugs into the barrel of the fountain pen and channels the ink from the cartridge or reservoir along tiny grooves that regulate the flow. It is carved into a shape that allows some ink to moisten its surface, creating surface tension that stops drops of ink from forming on the end of the nib.

In the early days, fountain pens did not have inbuilt ink buffers, with the result that ink flow was inconsistent. It would either run out of the pen and blot the paper, or it would dry up even though there was still plenty of ink. This was less than ideal, and many pen manufacturers searched for ways to correct the problem.

The purpose of a feed is to provide a controlled leak of ink onto the nib. The shape of the feed causes different pens to be wetter than others, i.e., it allows more ink to flow into the nib. Ink is drawn into the feed by capillary action because the channels along which it runs are so fine. The ink won’t flow from the pen unless the nib is touched to paper.

Two pens can vary significantly in the way they write simply because they have different feeds. A poorly designed feed may stop the flow of ink altogether. The shape and material of the feed are definitive of whether ink flows smoothly or not. Pens with a higher flow feel as though they are gliding across the paper, while those with a lower flow may feel scratchy.  The type of ink you use will also affect the ink flow as some pens work better with certain inks than others.

The feeds in older pens and more expensive ones are made from ebonite, a hard, vulcanized rubber, while others are made with injection-molded Acrylonitrile Butadiene Styrene (ABS). The roughness of the material used to make the feed affects how well it works.

The Evolution of Feeds

According to legend, in 1881, L E Waterman, then an insurance salesman, had a disastrous inkblot on a contract that cost him the sale. Angry and frustrated, he decided to devise a new feed by whittling at bits of hard rubber. He discovered a way to meter the airflow through the feed into the ink chamber by cutting a series of channels in the feed’s surface.

In 1883 he applied for a patent which was granted in 1884. In the patent, he deliberately did not specify the number of fissures in the feed to prevent others from getting around it by simply altering the number of fissures. His design was so successful he was soon making pens for his friends and then for sale to the wider public. Waterman pens are now world-famous, so he was definitely onto something.

In 1889 Waterman improved on his original design with the “Spoon feed” to buffer the ink flow irregularities that still occurred sometimes. For this new design, he carved wells along the feed channels in which excess ink could pool. When the flow from the reservoir abated, the ink would flow back out of the wells. Since he also patented the “Spoon feed,” his competitors were left scratching their heads for alternative solutions once again.

George S. Parker of Parker Pen Company fame responded in 1894 by inventing his famous “Lucky Curve” design. He tried out different methods that involved extending a protuberance on the feed further and further into the ink reservoir in the pen’s barrel. He found that extending a thin finger of material with a curved tip that touched the inside of the barrel provided a way for excess ink to drain out of the feed.

In 1905 Parker further refined his feed by cutting notches into the side of it. He patented it and called it his “Christmas Tree” feed. In 1910 pens with comb feeds started appearing with a series of serrations on the sides. Sheaffer in the 1930s made these cuts even finer.

In 1911, Kyugoro Sakata, an engineer from Hiroshima, was given a fountain pen by a sailor friend. Intrigued, he became determined to produce high-performance writing instruments in Japan. He called his company Sailor Pen, hoping his product would sail the seven seas and become internationally recognized. Any fountain pen enthusiast will tell you he succeeded beyond his wildest dreams as Sailor pens are some of the most sought after worldwide.

Since then, pen engineers have got to work and perfected several feed designs used in different modern pens. Some feeds are relatively simple, while others are more complex. Most feeds extend a way into the pen’s reservoir and serve as a cork to prevent unwanted leakage.

In the second half of the previous century, many new feeds were developed to accommodate ink cartridges and converters. These designs include a collector reservoir as well as the serrations below the nib.

What Is Capillary Action?

Capillary action refers to the drawing effect that small fissures have on a fluid. It is the movement of a liquid within the fine spaces of a porous material due to surface tension and forces of cohesion and adhesion.

Although a fountain pen feed does not soak up ink like a sponge because the material it is made from is not absorbent, its design allows it to hold ink until it is needed. The fine grooves and channels in a fountain pen feed are effectively pores along which the ink creeps by capillary action.

The fissure size affects the strength of capillary action, so it is quite an art to develop the right-sized slits for a feed. The fins are usually arranged perpendicular to the feed’s axis and fill up due to gravitational action from the lowest to the highest. When there is a surplus of ink, the fins’ capillary action must wick the ink away from the feed capillary before there is a noticeable change in the ink supply at the nib.

This requires a delicate balancing act in feed design. The feed must not only meter the amount of ink flowing to the nib, but it must also allow just the right amount of air to flow in the opposite direction into the reservoir to replace the used ink.


Modern fountain pens are works of precision engineering that are both functional and beautiful. Thanks to the fins and other features of ink feeds, inkblots and spoiled documents are largely things of the past. High-end pens still tend to have ebonite feeds, but their design is far superior to the one Mr. Waterman first created at his kitchen table more than a hundred and thirty years ago. 

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