Questions you've had, but never got around to asking. Fire away!

I figured it might be useful to have a topic for fielding and answering questions that members might have that they’ve never gotten around to asking (for a variety of reasons).

I’ll start it off.

Of course, as we all know the well known mechanical pencil (not holder) common lead sizes are 0.2, 0.3 0.4, 0.5, 0.7, 0.9, and 1.1. But I wonder if these designations are subject to slight variances.

My first question: Is all lead manufactured to the exact same precise diameter as labeled? Meaning, if you had a high precision measuring tool accurate to 0.01 mm, would test measurements of lead from a variety of major lead producing brands all yield the exact same diameter measurement for a given lead size? For example, might some show 0.50mm, but others show 0.49mm or 0.51mm? Or perhaps even wider variances?

Secondly, are all mechanical pencil tips bored out to a 100% precise lead size? Or are there variances to this in the 100th place, possibly as found in lead?

What this leads to is my last question, now that I’ve gotten these two questions on the table. Presuming variances in lead and bore diameter, is it theoretically possible you could have a mechanical pencil in 0.3 mm size that has a bored out diameter of 0.29mm, and you could by chance have 0.3 mm lead that actually measures 0.32 mm, and thus you’d find the lead presents undue friction or might not work at all?

Thanks for your input.


rOtring’s 0.3mm lead was originally 0.35mm in diameter. No idea if that’s still the case, but it was the case at one time. (Their pencils were labeled “0.35”.)


Hallo there.

Just a quick add-on (I’m drowning in commitments these days, and cannot write as much as I would like here and elsewhere): I’m definitely sure there is a variance in both lead diameters and bore machining (any physical measurement Z comes with an intrinsic error ∆Z, let alone when industrial processes are involved), but in recent times the risk of having such variance preventing lead from advancing in a pipe is quite tiny I think — both errors can be quickly fixed by just removing the wrong pieces somewhere along the assembly lines of the manufacturers.

Also, remember that what we now almost universally call 0.3mm diameter was once called 0.35mm (especially around Germany/Europe, see e.g. some old rOtrings and their imprints), and everything is still compatible today — I tested many boxes of old lead put into modern pencils — so I assume a variance of 0.05mm is peacefully tolerated by the MP’s overall ecosystem.

At the same time, I have a K+E ‘020’ Leroy twistaction pencil from the early sets of lettering templates, and it ought to work with modern 0.5 lead, but it doesn’t, and I’m starting to think I need to test it with my 0.4 batch, as the supposedly equivalent 0.5 lead doesn’t really fit the writing tip of the pencil (ok, it has its own small stock of original lead in a white plastic cylinder, but who might want to use that?).

Back in the good old days of semi-artisanal pencil-making, or just when industrial standardisation was not as widespread (up to the 50’s, perhaps?), the situation was quite different: I’ve recently found an old box of short pencil lead pieces for twistaction pencils by the Italian maker FILA (= “Fabbrica Italiana Lapis e Affini”, “Italian Manufacturing Company for Pencils and Assimilated Products”), and the diameters on the labels amazingly read “1.1mm”, “1.15mm”, “1.2mm”, “1.4mm”.

And if you’re wondering: yes, they do come in actually different sizes: the lead pieces were all mixed up, so I had to grab my vernier calliper, and divide the content of any tube into subsets, to later refill the tubes with the correct assortment — the variance was around 0.04 mm, once again.

There is an entire website, if I remember correctly, devoted to selling unusual size lead pieces, even though I think those would be considered “fatty” lead sizes compared to the ones of MP’s we mostly talk on this forum.

Finally, I think a variance of just 0.01mm is too tiny, and for actual errors in pairing up lead and pipe, the bare minimum today is around 0.06÷0.08mm, but this is just me wild-guessing here.


I’ve been down this rabbit hole.

There can be a huge variation between one manufacturers actual lead size to another’s and to the nominal.
Then what they actually call them, i.e. Rotring and their 0.3/0.35 and 0.9/1.0 designations


Don’t forget about the Tombow’s 0.6mm mp :thinking:


There are ISO standards ( ISO 20318-1:2019) for the lead sizes, darkness based on grade, and the amount of slip. I think that there are also JIS documents that cover these as well which may not be exactly the same.

There is an Indian standard document on the internet archive:


From ISO Standard. Note how what they call 1mm really is 0.9mm with both tolerances being negative. And 0.5mm is really 0.6mm.


When did 0.35mm come out in Germany/Europe?

Don’t know, actually; will try to gather some information on the matter.

It’s probably around the same time when the other debate — between 1.0 and 0.9 (as @Kiwi-d mentioned, and I forgot to quote) — was settled.

I’ll keep you updated.

1 Like

check these webpage:

In addition, there are 0.6mm lead from Tombow, 0.8mm lead from a Korea brand, and 0.1mm lead from that Pentel’s prototype.


Just curious, because I know that Pentel came out with 0.3mm in 1968 with the Mechanica. It was never called 0.35 in Japan.

1 Like

I started searching for more info in a couple of directions: old online catalogue scans, and physical specimens around my desk, hoping to be lucky enough to be struck by a date stamped somewhere.

Alas, no luck so far. But I found some other bits of information.

Apparently, the “0.35mm” label seems to be limited to certain brands, and even there only a few models stick to that convention; to name the few I could spot on the fly, in no particular order:

• Rotring 300 (black plastic body), older versions
• Rotring 600 (black metal body), older versions
• Faber-Castell TK-Fine (green plastic barrel), still for sale online
• Faber-Castell TK_FIne Vario L (metal grip, green plastic body)
• Rotring Tikky (various models, mainly white or burgundy plastic body), older types

I have here a Staedtler Marstechno sporting an interesting “0.3/0.35” silver foil imprint on the blue body with metal grip section, and this might be a “transitional” model, maybe?

Also, the “0.35” denomination rarely appear on lead containers: the only specimens I could find quickly were:

• A box-shaped container of Koh-I-Noor “Polymer” lead refills (white bottom with the word “JAPAN” slightly raised above the surface, transparent middle section, yellow cap), which is too similar to other containers i have, but those sport the “Tombow” logo;
• A classic blue tube of Staedtler Mars Micrograph Super Hi Polymer (no. 250 03) in 3H, where I can read both 0.3 and 0.35 (the former above the latter)

An finally, I have here:

• One container of — again — Koh-I-Noor “Polymer” lead refills (white bottom with the word “JAPAN” slightly raised above the surface, transparent middle section, orange cap) where the lead diameter is denoted as “1.0”;
• One container by Faber-Castell (dark green body, orange sliding cap) with the label presenting “1.0” on a top row, and immediately below also sporting “(0.9)” — brackets included, which I found so graceful.

Maybe (maybe) by tracing back these MP’s we can get to the first who had the idea to more precisely pin down the actual size of the lead. I’ll try to get some pictures of the lead containers later on.


Thanks! This chart is very useful and does confirm variances by as much as 0.03 mm.

Of course, the wider the lead diameter, the less this variance would be perceived due to the ratio. But it does pose some interesting considerations. For a pencil, the lead chuck’s dynamic nature would accommodate such variances, but the pencil nosecone is a different matter. And I wonder if makers incorporated some additional leeway to take this into consideration.

This would explain rOtring going with 0.35mm labels.

In keeping with their reputation for precision, Rotring has labeled the 0.3 mm lead as 0.35 mm, because standard 0.3 mm lead is actually closer to 0.35 mm in diameter .

1 Like

By the way: most underrated face-turns-heel-turns-face-again post of 2023. :smiley:

As for the lead pipe, refer to this:



I have a question that has been bouncing around in my head for a bit. If you were wanting to measure how much force it takes to click/knock a MP, could you measure it by pressing down on a scale (that is set to record the peak value) until it clicks?

Here is an example image but the AI refuses to draw the pen with the tip up, so imaging in this example the tip is pointing up and they are pressing the knock end down on the scale.

Would this be the easiest/cheapest solution to measure the force required?



Hmm. I don’t think that would give you an accurate reading of the actual force but it could give you a range of force needed if you test enough pencils.

I would use a digital push/pull force gauge to do this. There are super affordable force gauges available. You wouldn’t need the $500+ ones that are used for industrial testing.

In fact, this is all you need.


I have nothing useful to add and hopefully @Knockologist has the useful answer. I am just here to say that that picture has alot of subtle body horror going on.


LOL - yeah, I think professional artists can rest easily for the time being. AI generated art has a long way to go. But its sooo much better than my MS Paint and stick figure alternative.