Yeah, it's certainly pretty impressive.
I'm sure the same nib will fit any Chinese #6 nibbed pens. The J X750 certainly deserves it, it looks as if the nib is made for that pen.
I've used a Bock titanium nib in a Delta Titanio I was loaned a few years ago, and must admit I wasn't keen on the force needed to flex it, about 150grams force or thereabouts (I measured it by pressing on electronic scales). That's a good deal more than my vintage flex nibs and was quite tiring to keep up. Having a new one, can you comment on the force needed on the current nibs? It may have changed over the years.
more flexible < ------------------------------------------------------------------------ > less flexible
Zebra G dip nib > Bock Ti nib (#6 EF) > vintage Eversharp Skyline (gold nib) >. FPR flexible nib (#6 EF)
To me the #6 Bock Titanium nib is not difficult to use for everyday writing and it is not difficult to flex either. I would say this nib has been the most comfortable nib I have used in a fountain pen. Sorry I cannot use an electronic scales, still how would one measure how many microns the tines part when you a apply a certain force? Could be the force needed to remove a plastic shim inserted between the two tines. You need to standarize not only the force needed but also the distance the tines part under the same force, too much intra- and inter-examiner variability.
Still according to my own personal experience:
i) - Compared to a vintage Eversharp Skyline pen with a gold nib*, I would say that the #6 Bock Ti nib takes a perceptively less force to flex. This may also be due to the size difference between the two nibs, the skyline seems like a #5 size nib.
ii) - Compared to a FPR flex nib I had previously placed in another Jinhao x750, the FPR nib is considerably stiffer compared to the Bock Titanium.
iii) - Finally, the Zebra G nib is easier to flex and writes thinner than my Bock Ti EF. However, the Zebra G is originally a dip pen nib and it's tines also can very easily deform, this is has not been the case with the Bock nib IMO.
I hope this helps a little.
* Eversharp Skyline pen was a PIF loan from forum member Alexander_K from the Netherlands, Alexander, thank you very much for the pen, I really appreciate it.
Edited by Frank66, 11 December 2016 - 19:17.