Pentel S551 (Tentative Designation)

Not too long ago, I was searching for my favorite Pentel of all time: the PS535.

While doing so, I stumbled upon this one.

The clip, tips, and Pentel text are different from each other.

I searched for the fixed tip pencil in Nimrodd’s book and found it under the S551 name. It appears to be the precursor of the PS535, but found this auction suggesting otherwise.

My guess is that Pentel offered both pencils at the same time. The only change would be their tips and model numbers.


I have discovered I had 2 versions of the PS535 (with both of the above style text), and just today received a 3rd version of it.

I will be updating the book with the updated picture in a few weeks.

And if you look at the S551 in the book, it is the newer Pentel logo text, with the longer clip. I would appreciate if you could post a photo of the S551 on a white background that I could use in the book, to show both versions.

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Why does that auction suggest otherwise?

The pricing sticker—and Pentel’s general history—suggest the all-caps version came first, and then it was later replaced by the newer Pentel mark.

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Here you go.

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Yes, the all-caps Pentel logo did come first. I was referring how is the S551 doesn’t seem to be a precursor of the PS535 as the auction PS535 has the same text/clip suggesting the two models were manufactured during the same time period.

I must be missing something, because the pencil pictured in that auction listing looks precisely like I would expect that pencil to look.

Is there a clip mismatch or something? (Like, you’re expecting it to have that flat portion at the top of the clip?)

Bottom line: I don’t see what stuck out to you about this auction listing.

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The two pencils (PS353 and S551) are identical. The only change is in tip and model number. PS535s have sliding sleeve tip, S551s have a fixed tip. My point is, the auction pencil is a PS535 with the older logo and clip, showing the S551 doesn’t seem to be a precursor of the PS535 due to the identical bodies/clip. Basically suggesting they were manufactured around the same time as different models numbers. I hope you get what I’m trying to say. :wink:

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Yes, I understand, but here’s where I’m lost:

  • The auction doesn’t mention a specific model number, and it offers no direct comparisons between the PS535 and the alleged S551.

  • You mention the auction pencil is a PS535 with the older logo and clip; isn’t this what’s expected? The earliest versions were manufactured with the all-caps logo, and then later versions have the rounded sans-serif logo.

  • Given the above two points, I’m just not seeing how you’re deriving any information from the auction listing about relative manufacturing times. The only thing I can figure is you’re operating under the assumption the S551 came first. (If true, that would be news to me. Do old catalogs confirm this?)

• In Nimrodd’s Book (page 339), he infers the S551 Black Pencil is a “precursor to the PS535.” The S551 pictured in the book shows the pencil with the newer Pentel logo and clip.

• The S551 in this post contains the older clip/logo.

• The auction link shows a PS535 with the older clip/logo, disproving the inferences of the S551 being a precursor of the PS535.

My point: The S551 doesn’t seem to be a precursor of the PS535.

I hope this clears everything up.

Here is my take on this. The earliest models were the S551 which had the old logo, arched clip, and a fixed lead sleeve. These also had the 5mm diameter cap. There are differences in the mechanism and reservoir. The last model PS535 had the new logo, flat top clip, black plastic reservoir, sliding lead sleeve, and a 6mm cap. There were likely some transitional models that had the sliding sleeve, old logo and the smaller diameter cap. Clearly Pentel used things up and never threw things away just because they had the old logo.

I do know that the tip from the later PS535 does screw onto the end of the S551, but it does not match cleanly with the grip. So there is some differences between the generations at both ends of the pencil.

The S551 did precede the PS535. They may even have been in production at the same time. Without primary (or even good secondary) sources it is not possible to be certain. There is some variation in both models and that could be reflected in the book.


It appears that both the S551 and PS535 originally came with the old logo (type-face Pentel) and the metal reservoir.

Later they both came with the new style Pentel logo and changed to a plastic reservoir.

Even later the PS535 came where they dropped the “5” and replaced it with “0.5”. I just received these yesterday. I could not find a date code on these to determine when they were made. They do have the plastic reservoir.

I have updated the S551 photo for a later version of the book, thanks to Cummins07.

I also discovered that I did have the older version of the PS535, and the current versions, so I will be taking a new photo of that with all 3 generations for the book.

I will update the information on both the S551 and PS535 in the book.


Ah, ok, I’m not sure I’ve ever agreed with that assertion from the book. Hence, I wasn’t using that as a “given” in my calculations.

In other words, I have never bought into the idea that the S551—if that was even a legit model number—was a precursor to the PS535.

Again, the book is a Work-in-Process, and I was basing it on information I have.

I should have just kept the S551 as an Unknown Model - we based the number off the ML5/ML51 system. I don’t remember why we thought it was earlier, as there is absolutely no information about it.

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I like how the book documents Jimmy’s current understanding and thoughts based on his research and our contribution. It’s a living, breathing, and changing document. I love it.

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I have never been happy with the S551 designation and am thinking about reverting it to Unknown Model 02 (that was never publicly released in the book). What do you guys think? The index would keep the S551 pointing it to the Unknown Model 02 page.

Here is what I am thinking to re-write the Unknown Model 02 (S551) Black 5 Pencil description:
"This pencil appears to have come out concurrently with the PS535, at least through the first 2 generations. It uses the same body/grip (S55 ridged grip), with the silver ring at the bottom of the body that is notched out for the name Pentel, but has a fixed tip.
On the first generation, the Pentel is in the old type-face font, has a shorter, rounded clip and the pencil reservoir is aluminum (or some metal alloy). The second generation switched to the current Pentel logo and has a longer clip that is flattened at the top. The pencil reservoir is made of plastic and is a common reservoir among many Pentel pencils.

For a while we had this pencil designated as S551. Our thoughts on this were since this was based on the S55 with the black body, and the ML51 was a black body version of the ML5, we just added the 1 after the S55. I have never really been fond of that designation, and have reverted it to Unknown Model 02."

And here is the re-written PS535 description:
"This pencil has the same ridged grip as the S50 series. The most distinctive thing about this pencil is the black body with the silver ring at the bottom that is notched out for the name Pentel.
On the first generation, the Pentel is in the old type-face font, has a shorter, rounded clip and the pencil reservoir is aluminum (or some metal alloy). The second generation switched to the current Pentel logo and has a longer clip that is flattened at the top. The pencil reservoir is made of plastic and is a common reservoir among many Pentel pencils. The third generation appears to be the same as Generation 2, with the exception that Pentel removed the “5” logo, replacing it with “0.5”.

It is related to the Unknown Model 02 Black 5 pencil (same pencil with a fixed tip)."


I think it should be unknown, as the S551 designation is purely inferential. Since I first learned of its alleged existence, I have maintained that it was a Frankenpencil with a different tip applied before it was sold in secondhand markets.

I suppose the pencil should be abandoned altogether based on this reasoning. I think it’s always been the PS535, and that pencil has simply gone through 2 significant changes (logo + clip, and then the 05 logo).

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The S551 designation is likely my fault. It is the rationalized designation I used when cataloging these pencils in my collection.

We do have documentation on the existence of the model in the Japanese 1970 one sheet. This sheet does not show any sliding sleeve models. The fact that the S551 was produced before the PS535 is pretty obvious given the primary sources.

One bit of information that would clear things up some would be the date of the introduction of the sliding sleeve. Do we know when Pentel first produced a pencil with one?

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Sometime during the second generation of the PS535, Pentel switched from metal lead reservoir to plastic. The left one has no stamped manufactured date. The one in the right was made in 1986.

They also changed brass chuck. To the left (metal lead reservoir), the chuck is fully threaded. The right one (plastic lead reservoir) has a part where the thread is cut.

Eraser caps have a minor change too. Left is the one from the metal reservoir, right is from the plastic reservoir.

When would Pentel change from metal over to plastic lead reservoirs in the second generation? I suspect it occurred between 1979 and 1983. Why do I say this? Below is a PS45 and PS65, which is part of the family of 2mm Sliding Sleeve pencils the PS535 belongs to. The dates between 1979 and 1983 would match the timeline of my plastic reservoir one that has the 1986 date.


Point 1 - We have the Unknown Model 02 (S551) was in the 1970 Japanese one-sheet, so it probably came out in 1969-70, especially since the Gen 1 version used the type-face Pentel.

Point 2 - The PS535 Gen 1 has the same body and grip as the UM02 above. Now, Pentel may have made a bunch of bodies for the UM02 and had them sitting around for a few years before they made the first PS535, or they could have started them in 1970 (after the one-sheet was printed).

Point 3 - The PS1042 (and probably PS1045) came out in 1973.

Point 4 - The PF335 & PF337 were out by 1975. I do have a PF335 that could POSSIBLY be a Gen 2 - it has the raised text on the bottom and no text on the side, but that could have been wiped off over the years (making it a Gen 3). Gen 2 P200 pencils are, best guess, circa 1971-74.

So, the only definitive date we have for a Sliding Sleeve is 1973 (for the 0.2mm), but that does not preclude 0.5mm or 0.7mm being out before that.