From the Knockology archives
This post revisits conversations from our smaller community before we moved to this forum. I’ve brought the discoveries and memorable moments together, with credit to the members who contributed. These discussions reflect what we knew at the time. Please add any newer information, corrections, or photos below!
A cracked pocket clip sent me looking at twenty Pentel PD335s, and the most suspicious part turned out to be the eraser.
That is how a small annoyance becomes a twenty-pencil comparison around here.
Same model, different erasers
The PD335 came with and without Pop’n’Pop branding. They are versions of the same model, which gave me a useful comparison when I noticed cracking on some of the Pop’n’Pop examples’ plastic pocket clips.
I measured ten Pop’n’Pop PD335s and ten regular, non-Pop’n’Pop PD335s, checking both the erasers and the openings that held them.
Here were the averages:
| Measurement | Pop’n’Pop PD335 | Non-Pop’n’Pop PD335 |
|---|---|---|
| Eraser opening | 7.242 mm | 7.229 mm |
| Eraser diameter | 7.32 mm | 7.15 mm |
The openings were nearly the same size. The erasers weren’t.
The original eraser comparison from January 2022.
In the Pop’n’Pop group, the average eraser diameter was larger than the opening holding it. The regular PD335 group showed the opposite relationship. That made eraser fit a plausible suspect for stress on those aging plastic clips.
The photograph supplied another clue: the green erasers looked different, too. In the original discussion I said I had looked through a few dozen examples and kept seeing that appearance on the Pop’n’Pop erasers.
Had they grown, or started too large?
That was the question the measurements could not answer. Perhaps the erasers had expanded with age. Perhaps they had been slightly oversized from the beginning. Not every Pop’n’Pop clip was cracked, and we had not isolated the cause of every failure.
The table records my sample averages, not factory specifications or guaranteed tolerances. I am keeping the original numbers, but three decimal places should not suggest more measurement accuracy than the exercise established.
Still, we now had a way to compare the problem: look at the PD335 version, the eraser, the opening and the damage together. A different replacement eraser or an unknown storage history could complicate an individual example, so those details belonged in the notes too.
My verdict at the time was rather less cautious:
“The damn erasers are different and too big. Case closed :)”
Which was probably giving “case closed” a little too much credit.
Knocktype11 raised another possibility:
“I wonder if the Popn’pops were made at a different location. It might also be a different lot of erasers. Anyway I have removed the erasers from my PD335s.”
A different batch seemed a plausible explanation for the differences I was seeing, although we hadn’t confirmed the manufacturing history or material composition. Knocktype11 had already decided what to do with his examples: the erasers were coming out.
The cause was not settled, but the next person with a cracked clip had something specific to check. And a very small piece of green rubber had managed to turn twenty pencils into a research project.
Knock on!