Hello Craig,
As has been said above, they will write a little differently. A Jowo #6 M won't be the same as a Bock #6 M, but it is going to come down to personal preference.
The Bocks do come in some other finishes that are pretty neat, like Black, Red and Purple Lacquer. Check them all out here on
Beaufort Ink's site.
I will share my thoughts from a maker perspective, but will tell you others here have far more experience than I do.
I have the drills and taps for both. I have made sections for both. The biggest issue that I have experienced, and have read about (and listed about on the "As the Pen Turns" podcast), is that the with the Bock #6, the drill hole/tap/threads are slightly larger and they are farther back on the nib housing. This means that they are deeper into the section, and closer to the section tenon, which translates into a thinner material near the section tenon and increases the probability of breaking the section during making or after.
Here is a quick photo I took of both nibs and a section. You can see how much closer the threads on the Bock are to the section tenon, it definitely creates a week spot and I have had them fail as I am making them far more frequently that with making Jowo sections.
I hope that this makes sense. Let me know if it does not.
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