Skip to content

A Bock Mystery

Posted in Fountain Pens

Last week, I posted on Instagram, sharing an interesting situation. The Kawari-Nuri and Nashiji Nuri pen I own from Tamenuri Studio takes Bock #6 nibs. For this particular use of it, I decided to put the new cat-engraved nib from Shibui North into it.

Unfortunately, to my surprise, it didn’t fit! Both nibs are Bock #6, with no sign of damage to the housings. And there started the mystery I have found myself enmeshed in now. Why didn’t both nibs fit? And, when I tried a couple other nibs, why didn’t they fit?

Because I shared this on Instagram, I felt it was worth following up. And, the amount of feedback I received and the research I did means it needs more than an Instagram post to cover everything.

CAVEAT: I am not an expert on Bock nibs, nib housings, or even nibs in general. I’m only sharing information I gathered after posting about an issue I came across last week. I have done my best to not make any hard claims, as I really can’t say what’s going on here.


My Instagram post got more comments than I expected. While many were along the lines of, I need to check my nibs or oh no, I did get quite a few comments from makers. I shortened some of the comments below to share the salient points. Please see my post to read the full comment threads.

From Loft Pens: Oh wow, I thought I was going crazy or my material was dodgy as at at some point the nibs just became tighter and tighter to put in

From Butter Knife Creations: The tapco tap has changed! Which is and was weird so you need to adjust the depth of the cut for the tap itself. Bock housing are good I believe… I bought a new tap about 6 months ago… My old tap was 6ish years old.

From Hinze Pen Co: Hey y’all… The housings have not changed, some of the tooling out in the wild do not cut the threads to the same depth, and that’s the crux of the issue… If [the nib] was forced into a smaller housing (thread) and removed multiple times, wear will dull.thr thread crests allowing it more places. The material of the section can also introduce wear (metal vs. Plastic, and then various plastic polymers. The housings have not changed

It was this last comment thread that really got me thinking. I’d only tried a few nibs in a single pen. To me, that was hardly enough to claim there was a problem with the pen. Although, I must also admit that I was precipitate in declaring a problem with Bock housings.

Time for Data!

Data hoarder that I am, I needed data. So, I took twelve measurements from seven different housings. I also tried those seven housings in four different pens. While still not enough data to determine what was wrong, it was better than what I had previously. But, the results were… unexpected to say the least. I suggest you look through the data tables to see for yourself, but, you can also jump down to my thoughts if you prefer.

Measurement Locations

I attempted to measure everything I could think of that might make a difference to how a housing fits in a section. I used the same, admittedly inexpensive, caliper for every measurement. In case my location descriptions don’t make sense to you, I’ve also provided a lovely technical drawing.

  1. Diameter under the top lip
  2. Diameter under the indents
  3. Diameter directly under the step down
  4. Diameter of the threads
  5. Diameter of the step down under the threads
  6. Height of the housing, including the “nub” at the bottom
  7. Height of the housing, without the “nub”
  8. Height of the upper section of the housing, before the first step down
  9. Height of the lower section of the housing, from first step down to base, not including the “nub”
  10. Height from the first step down to the threads
  11. Height of the threads
  12. Height of the smooth portion directly under the threads
vector technical drawing showing the measurement locations on the Bock housing.
Click the image to view full size if you have any trouble reading the numbers.

Housing Measurements

I took each of the measurements listed above for each housing. I used the widest variety of housings possible given my and Jim’s collections. But, both of us have collections that favor Jowo nibs.

  • Housing 1: Nib and housing that came with the Tamenuri Studio pen in question, purchased in September 2021
  • Housing 2: Nib and housing that came with a pen purchased in June 2021
  • Housing 3: Ebonite housing Jim had that is a few years old
  • Housing 4: Clear plastic housing Jim had that is a few years old. * Because this housing does not have a step down, I took measurement 3 directly above the threads, and measurement 8 is the length from the top lip to the threads.
  • Housing 5: Oblique nib and housing purchased in November 2022
  • Housing 6: Kitty nib and housing purchased in November 2023
  • Housing 7: New nib and housing that came with a pen purchased in December 2023
Msmt.Housing 1Housing 2Housing 3Housing 4*Housing 5Housing 6Housing 7
17.9mm7.9mm7.8mm f2b
7.9mm s2s
7.8mm f2b
7.9mm s2s
7.7mm f2b
8.0mm s2s
27.9mm f2b1
7.8mm s2s2
7.9mm f2b
7.8mm s2s
7.8mmNo step down7.9mm f2b
7.8mm s2s
7.9mm f2b
7.8mm s2s
37.4mm f2b
7.3mm s2s
7.3mm7.2mm7.8mm f2b
7.7mm s2s
7.4mm f2b
7.3mm s2s
7.4mm f2b
7.3mm s2s
7.4mm f2b
7.3mm s2s
47.7mm7.8mm f2b
7.7mm s2s
7.7mm7.8mm f2b
7.7mm s2s
56.6mm f2b
6.5mm s2s
6.6mm6.6mm6.7mm f2b
6.6mm s2s
6.6mm f2b
6.5mm s2s
6.6mm f2b
6.5mm s2s
99.0mm8.9mm9.4mm– –9.0m9.0mm9.0mm
105.0mm5.0mm5.4mm– –5.0mm5.0mm5.0mm
1. Front to Back (f2b). 2. Side to side (s2s)

Housing Fit

Having measured all of the housings, I tried them all in various pens Jim and I have that take Bock nibs.

  • Pen 1: Tamenuri Studio, purchased September 2021
  • Pen 2: Karas Kustoms, purchased before 2020
  • Pen 3: Chicago Pen Co, purchased June 2021
  • Pen 4: Den’s Pens, purchased October 2023
HousingFits in Pen 1Fits in Pen 2Fits in Pen 3Fits in Pen 4
2NoYesYesYes, but slightly tight
5NoYes, but tightYesYes, but tight
6NoYesYesYes, but tight
7NoYesYesyes, but tight

360° Views

Because it was mentioned that maybe the housing had been forced into the pen, I decided to take close up videos of each housing.

There are some scrape marks on the space between the threads and step down on Housing 1, but there doesn’t appear to be any damage to the threads. I don’t think — I could be very wrong — that the scrape marks are deep enough to make the difference between a nib that spins in easily and one that dead stops on attempting to screw it in.

The other housings, aside from some grime, also appear to have pristine threads. There are some general use scrapes along other parts of the housings, but, again, I don’t think that would make any difference.

My Thoughts

So, as I said before, unexpected. There doesn’t appear to be any correlation between measurements and whether a housing will fit in a pen. Nor do any of the nibs appear to have damage to the threads, including the original housing that came with the pen.

Had only the housing that came with the pen fit, I would consider it likely a problem with the pen. However, having found a second housing that fit, specifically one that I know is older, makes me doubt the pen problem theory. But, with other older pens able to take all of the nibs, it also makes the housing problem theory unlikely.

So, I’m left unable to say more than, “I don’t know.” The more data I gathered, the more questions — and less answers — I had. I don’t know enough about pen making, taps, dies, and necessary clearances to figure this one out. Nor do I have the equipment necessary to take a look at the threads inside the section in question.

For now, I can only say that if you have pens that take Bock or Jowo nibs, it may be worth testing other nibs in them before buying a new nib.

I’d love to hear your opinion on what the problem might be. I haven’t the slightest idea at this point, so your guess is as good as mine.

But Wait, There’s More!

So, after I finished writing this, Jim found a post on that may share the root of the issue. It was posted in September 2021, which is the right time period. I suggest you read the blog post, but the TL;DR version is that there was one or more tap — a tool to cut the inner threads of a cylinder — available that was defective.

Is this the definitive answer? I can’t say, but it seems likely. I still don’t quite understand how any issue means that some housings fit and some don’t when none of the housings appear to have any modification or damage. But, it’s OK, I’m not necessarily looking to understand right now.

Have you had this problem with any Bock housings? Please let me know in the comments.

Thanks for reading to the end, I hope you enjoyed my post. Make sure to subscribe to my blog or follow me on Instagram so you don’t miss any posts. I generally post at least once a week.


  1. Hi,
    I’m the person who wrote the blog posting at

    Just for your information:
    – The tap that didn’t work for me was an M7, 9 x 0.6 6H
    – The corrected size is M7, 9 x 0.6 6H+3

    There was a lot of back-and-forth with about this, and I was happy that Pablo finally solved the problem and replaced his stock with taps that work with the Bock 250 housing. I don’t know if the source of information that resulted in the original tap can explain why you’re seeing the differences, but it could be.


    January 17, 2024
    • Hi Geoff, thanks for chiming in!

      January 17, 2024

Leave a Reply

Your email address will not be published. Required fields are marked *