The curious arithmetic of mechanical pencil refills

Pentel Ain lead refills

Hmm, has anyone noticed this aspect of mechanical pencil refills?

Pentel Ain refills (just to pick a particular brand) are all the same price.

And all are 60mm in length.

But they contain:

0.3mm – 20 pieces
0.4mm – 30 pieces
0.5mm – 40 pieces
0.7mm – 40 pieces
0.9mm – 36 pieces

What gives? Thinner lead costs more? I would think one would get more pieces of thin lead per dollar.

If you calculate volume = length * pi * radius * radius

Then single pieces of lead are:

0.3mm = 60mm * 3.14 * 0.15mm * 0.15mm = 4.24mm3
0.4mm = 60mm * 3.14 * 0.20mm * 0.20mm = 7.54mm3
0.5mm = 60mm * 3.14 * 0.25mm * 0.25mm = 11.78mm3
0.7mm = 60mm * 3.14 * 0.35mm * 0.35mm = 23.08mm3
0.9mm = 60mm * 3.14 * 0.45mm* 0.45mm = 38.16mm3

That’s right – a 0.9mm lead is 9 times the volume of a 0.3mm lead! (Which makes sense as the volume is proportional to the square of the three-times-larger radius.)

So as to how much lead is in a Pentel Ain box:

0.3mm: 20 * 4.24mm3 = 84.80mm3
0.4mm: 30 * 7.54mm3 = 226.20mm3
0.5mm: 40 * 11.78mm3 = 471.20mm3
0.7mm: 40 * 23.08mm3 = 923.20mm3
0.9mm: 36 * 38.16mm3 = 1373.76mm3

That’s right – for the same price, a 0.9mm user gets 16 times more lead in a box than a 0.3mm user!


Mechanical pencils for puzzles

Mechanical pencils for puzzles

In 2006, Dave’s Mechanical Pencils had a great review of some interesting puzzle pencils from Retro 51 – mechanical pencils decorated with puzzle images.

Here are two more. I’ll mention that they are sold at much lower price points than Retro 51’s offerings.

Mechanical pencils for puzzles

The Xonex Crossword pencil and Autopoint Sudoku pencil both convey fun and practicality – bold graphics, and uncapped oversize erasers (unusual in mechanical pencils), for those of us who like to be able to correct our mistakes.

The Autopoint features 0.9mm lead, with a tube of B grade refills and three replacement erasers. It is made in the USA.

Mechanical pencils for puzzles

The Xonex has a more modern 0.7mm diameter lead, with unstated grade refills, and six replacement erasers. It is made in Taiwan.

Mechanical pencils for puzzles

Both seem solid, and good values for their price. The Autopoint is thinner, longer, and more traditional in appearance. The Xonex is definitely on the modern side. I also like the Xonex’s vinyl eraser, though the grey Autopoint eraser also works quite well!

Mechanical pencils for puzzles

Mechanical pencils for puzzles

Their packaging is not as elaborate as that of the Retro 51 (especially the near-generic Autopoint), but either would make a fine gift.

Hayakawa tribute pencil

In 1915, Tokuji Hayakawa invented the “Ever-Sharp” or “supply-type” mechanical pencil. Along with a belt buckle and water faucet, it was part of a stream of inventions that launched what would become the Sharp Electronics company.

The pencil was not well received at first – Sharp’s website mentions that the pencil was said to feel cold in winter, and clash with Japanese clothing in appearance. Still, Sharp claims overseas orders led to success. (Though US success is questioned in an article by fountain pen dealer Mr. Nishimura of

The pencil received a US patent in 1926:

Platinum Hayakawa tribute pencil

Platinum Hayakawa tribute pencil

The story is tinged with deep tragedy. The Great Kant? earthquake in 1923 killed Hayakawa’s wife and children, as well as destroying the factory. The rights to the pencil were subsequently sold.

Platinum Pen Co. has decided to celebrate this history with a reproduction of Hayakawa’s seminal pencil. I don’t know if Platinum has a formal relationship with Sharp or other firms that dealt with Hayakawa. The pencil doesn’t seem to be widely available, and I can find no mention on Platinum’s website.

The pencil is presented in a very plain yet elegant wooden box.

Platinum Hayakawa tribute pencil

Platinum Hayakawa tribute pencil

The spirals, cap, and two-tone clip are all prominent features. One can read “Platinum Japan 0.5” in fine lettering.

Platinum Hayakawa tribute pencil

Platinum Hayakawa tribute pencil

The 0.5mm lead is advanced by twisting the cap. The original pencil no doubt used a wider lead.

Platinum Hayakawa tribute pencil

The balance point seems a bit higher up than other pencils I am familiar with.

Platinum Hayakawa tribute pencil

I have no idea about the internal mechanisms, and if they reproduce the original.

Platinum Hayakawa tribute pencil

The pencil handles and writes well, and the shape is certainly more comfortable than expected. I don’t know if the dimensions match the original.

Platinum Hayakawa tribute pencil

I applaud this tribute to Mr. Hayakawa’s creation and the history of the mechanical pencil. The lettering and lead diameter (I hope) distinguish the pencil from the original.

References and further reading:

1. Platinum Pen Company

2. Hayakawa’s US patent Note: the document is in TIFF format, which requires special software to read.

3. A Tale of Two Pencils: Keeran’s Eversharp & Hayakawa’s Ever-Ready Sharp

4. Sharp Electronics page on Hayakawa’s pencil

5. Osaka Business Update, Vol. 3, 2006 – Great People of Osaka

January 13, 1952 (Yard-O-Led pencil)

January 13, 1952  (Yard-O-Led pencil)

I’m not sure what was being commemorated fifty-six years ago today, but that’s the date inscribed on this vintage Yard-O-Led pencil.

Engraved pens and pencils typically have names or initials, but this one has a date. I imagine it being a birth, a graduation, an anniversary, or some other milestone of life that was being commemorated. Yet, it’s still odd to me. If you chose a gift like this, and chose to have it engraved, wouldn’t you put the person’s name on the gift?

The pencil is rolled gold in a barley pattern with a hexagonal body. It takes a 1.18mm lead. I bought it mainly to inform myself about Yard-O-Led pencils, as I’ve thought of acquiring one of their new pencils.

While almost exactly the same length as a Lamy Scribble (which I find very comfortable), this pencil is too short for the way I want to grip it. I want to hold the hexagonal part of the body, just as I would a woodcase pencil. But this winds up causing the cap of the pencil to hit my hand in an uncomfortable way.

As to the lead and mechanism – I could not at all figure out how to adjust the lead. I kept looking at the instructions over at Dave’s Mechanical Pencils. My results at times resembled parts of a Marx Brothers comedy. At one point the lead shot out of the pencil across the room. Now let’s be fair and acknowledge that this pencil is over a half century old, with provenance unknown. It may have spent twenty or thirty years in a damp basement or a humid yurt. Removing the slider from the barrel was challenging – it just wouldn’t move beyond a certain point. But it did come out.

January 13, 1952  (Yard-O-Led pencil)

That “slider grip” is the oddest piece. Being new to this pencil, and having noticed that it can shoot parts around a room (due to a capable spring), I was alarmed when the slider “disappeared”. It was there – then it was gone. I feared it was snapped off, or sprung into the yonder. I couldn’t find it. I did notice that the other bits of the mechanism – the piece that holds the lead in particular – were also gone. At this point, I was thinking that I’d broken the pencil. I tried fishing around the slider barrel (which has a narrow opening) with an eyeglass screwdriver. There they were – the parts were submerged, and with some toggling, re-emerged. I carried on, and can say – it all works, and I can now retract and extent the lead, and know how to refill it. As far as I can tell, my original problems were due to the “refill nut” (another unfamiliar pencil part) not being properly in place. It wasn’t my focus, but after it being properly fastened, the pencil started to work – from the point of view of the cap, clockwise motion extended the lead, and a counter-clockwise motion retracted the lead. That’s how it should be!

As Dave wrote, “Complicated or what!”

If I ever buy a new Yard-O-Led pencil, it will be in person so that I can try out the feel.

But – I’m still wondering, what happened fifty-six years ago today?

Lamy ABC

The Lamy ABC pen and pencil set.

The Lamy ABC is a pen and pencil set aimed at children, though adults will have no difficulty enjoying these nicely made products.

The fountain pen is essentially a Lamy Vista in a pleasing wood and red plastic case. It takes Lamy cartridges or a converter. My version has a medium nib. It’s a tremendous value as fountain pens go – a great writer, smooth and highly reliable. The cap doesn’t post, which could be an issue for some, and has a space for a sticker with one’s name. It is really lightweight, even compared with a Vista, so it’s no trouble to transport around town.

Matching the pen is a mechanical pencil with a 3.15 mm lead. Unlike most clutch leadholders, which require pressing a button or cap and sliding the lead, this pencil has a really nice twist mechanism. Even Lamy’s more sophisticated looking (and expensive) Scribble 3.15 mm pencil doesn’t have this mechanism. There is also an included lead sharpener, which I love as it works with other 3.15 mm pencils, and is a pretty unusual sharpener.

3.15 mm lead of the Lamy ABC.The pencil is comfortable and writes very nicely. The lead is solid and doesn’t break. Though they ship with an HB lead by default, the pencils also take other hardnesses as well as colour leads from art supply stores.

It’s a mechanical pencil that offers great quality, as well as nice (though not traditional) styling.