uni Nano Dia Lead: Grades, Counts and Strength

uni Nano Dia 0.5 mm lead refill: a clear case with a black cap and three loose 60 mm (2.4 in) leads drawn to scale; inset: graphite with nano-diamond particles mixed in — Leads drawn to scale at 60 mm; the case is drawn by eye.

Product facts

Product: uni Nano Dia mechanical pencil lead (uni0.5-202ND HB, 0.5 mm, 40 leads)
Brand: uni
Brand origin: Japan
Made in: Not stated^*
Material: Graphite blended with nano-diamond particles
Released: 2008^*
Price range: $under $5 per item

Notes on these facts

Made by Mitsubishi Pencil Co., Ltd.. Country of manufacture not stated: Mitsubishi Pencil's pages we could reach and the Amazon US listings don't state where the standard black Nano Dia is made. Tacto Studio lists the related Nano Dia for Textbooks lead as made in Japan, but that is a different product, so we don't carry it over. Price: example listing. Released: Mitsubishi Pencil describes the Nano Dia series as a long seller since 2008; we found no exact launch date.
Price bands are typical US retail, checked October 2026. Conversions to US dollars are approximate, at October 2026 rates (US$1 = ¥158 = ₩1,330 = NT$32.5 = CN¥6.7 = SEK 9.9 = DKK 6.7 = ₺49.6 = C$1.41 = A$1.43; €1 = US$1.12; £1 = US$1.32; CHF 1 = US$1.21).

Key takeaways

Amazon US lists the 0.5 mm black Nano Dia at 40 leads per case, each 60 mm (2.4 in) long.
Mitsubishi Pencil's Japanese site lists ten 0.5 mm grades, from 4H to 4B, at ¥220 (about US$1.40) a case, including tax.
Mitsubishi Pencil says Nano Dia has been a long seller since its 2008 launch.
Nano Dia Color, an erasable colored lead, came in 0.7 mm in November 2014 and in seven 0.5 mm colors in 2016, at 20 leads a case.
A case sells in our $ band (under $5) in the US.

What is uni Nano Dia lead?

It’s Mitsubishi Pencil’s premium refill lead for mechanical pencils, with nano-sized diamond particles blended in. Mitsubishi Pencil’s Japanese site says the diamond makes the lead harder to break under heavy pressure and lets it write smoothly and clearly.

Mitsubishi Pencil calls Nano Dia a long seller since its 2008 launch. In the US, it’s one of the two premium leads Unsharpen’s lead guide recommends, alongside Pentel Ain Stein, and Amazon sells it by the case and in 10-case packs.

uni Nano Dia specs

Spec	Value
Maker	Mitsubishi Pencil Co., Ltd., Tokyo (brand: uni)
Product code	uni0.5-202ND (0.5 mm); order code U05202NDHB for HB
JAN (0.5 mm HB)	4902778030486
Leads per case	40 (0.5 mm, black)
Lead length	60 mm (2.4 in)
Grades (0.5 mm)	10: 4H, 3H, 2H, H, F, HB, B, 2B, 3B, 4B
Other sizes	0.3 mm (2H, H, HB, B, 2B), 0.4 mm (H, HB, B, 2B), 0.7 mm (H, HB, B); counts not confirmed
Japan list price	¥220 (about US$1.40) incl. tax per case
Launched	2008 (series)

The 40-lead count and 60 mm length come from Amazon US listings; grades and price come from Mitsubishi Pencil’s Japanese site. Mitsubishi Pencil’s page lists every item as Eco Mark certified. We couldn’t confirm lead counts for sizes other than 0.5 mm, and the page doesn’t state counts at all.

One uni Nano Dia 0.5 mm lead drawn to scale at 60 mm long and 0.5 mm thick, and the ten 0.5 mm grades from 4H to 4B as swatches darkening toward 4B — Ten grades in 0.5 mm, all in 60 mm leads (swatch tones illustrative).

Which grade should you buy?

Start with HB, and switch to B or 2B if you want darker lines with less pressure. Softer grades write darker but wear faster and smudge more; H grades stay sharp and light.

Nano Dia’s ten 0.5 mm grades go further than most US multi-packs, from 4H for very light construction lines to 4B for sketching.

Is Nano Dia really stronger?

Mitsubishi Pencil says so, but we found no independent breakage figure. The maker’s claim is that the diamond particles resist breaking when you press hard, which matters most in thin leads such as 0.3 mm.

Looria’s summary of about 20 reviews lists break resistance and the range up to 4B as positives. We haven’t measured it ourselves.

What other Nano Dia leads are there?

Mitsubishi Pencil sells colored and textbook versions under the same name.

Version	What it is	Facts
Nano Dia (uni0.5-202ND)	Black graphite lead	40 leads, 60 mm, 4H–4B
Nano Dia Color	Erasable colored lead	0.7 mm red and blue from November 2014; seven 0.5 mm colors from 2016; 20 leads
Nano Dia for Textbooks	Lead for glossy, coated paper	0.5 mm, 40 leads, 60 mm (Tacto Studio)

Mitsubishi Pencil says the color leads erase cleanly with an ordinary eraser. It also built a pencil around them, the uni Color, launched December 28, 2017.

Is Nano Dia worth the extra cost?

For most people, yes, if lead breaks or faint lines bother you; the difference in price is small. At ¥220 (about US$1.40) a case in Japan, a premium lead costs only a little more than an everyday one, and a case of 40 lasts a long time.

If you rarely break lead and write lightly, a basic lead works fine. The upgrade matters most for heavy-handed writers, for 0.3 mm pencils, and for people who want darker lines from a harder grade.

How should you store and load it?

Keep the case closed and load a few leads at a time. Loading too many leads into a pencil’s reservoir can jam the clutch, so two or three is plenty for most pencils.

Always match the lead diameter to the pencil: a 0.5 mm lead in a 0.7 mm pencil slips, and a 0.7 mm lead won’t fit a 0.5 mm one.

Which pencils does it fit?

Any mechanical pencil of the same diameter. The 0.5 mm leads suit everyday pencils such as the uni Kuru Toga, the Pentel Sharp P205 and the rOtring 600.

Where is uni Nano Dia made?

The listings we found for the standard black lead don’t say. Tacto Studio lists the related textbook lead as made in Japan, but that is a different product. Mitsubishi Pencil, the maker of uni, is based in Tokyo.

Frequently asked questions

How many leads are in a uni Nano Dia tube?

The 0.5 mm black lead comes 40 to a case, per Amazon US listings. Nano Dia Color cases hold 20 leads.

Is there really diamond in Nano Dia lead?

Mitsubishi Pencil says it blends nano-sized diamond particles into the lead so it resists breaking under pressure and writes smoothly and clearly. We haven't analyzed the lead ourselves.

What grades does uni Nano Dia come in?

Mitsubishi Pencil lists ten grades in 0.5 mm: 4H, 3H, 2H, H, F, HB, B, 2B, 3B and 4B. US shops mostly stock HB, B and 2B.

How long are uni Nano Dia leads?

Amazon lists the 0.5 mm leads at 60 mm (2.4 in), the standard length, so they fit any 0.5 mm mechanical pencil.

Nano Dia or Pentel Ain Stein: which is better?

Both are premium leads sold on strength and smoothness, and Unsharpen names them as the two to upgrade to. We haven't run a side-by-side test yet.

Can you erase uni Nano Dia Color lead?

Yes, Mitsubishi Pencil says the Nano Dia Color leads erase cleanly with a regular eraser, which is their point compared with colored pencils.

Where is uni Nano Dia lead made?

The listings we found for the standard black lead don't say. Mitsubishi Pencil is based in Tokyo, Japan.

Sources (12)

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