Diamond 580, 530 and 540 (and variants, eg 580AL, 580RB etc)
One of the advantages of the the TWSBI Diamond series is that replacement nib units are available and easily changed. All these models use a number 5 size nib. Although TWSBI has changed manufacturers (Schmidt for the early 530s, later Bock and now JoWo) all these nibs are interchangeable so the current Diamond 580 nib unit will fit the older 540 and 530 models. The only difference is that the current 580, 580AL and 580ALR models have a different front section with a metal trim ring but the innards are essentially the same so you can use a TWSBI Diamond 580 replacement nib on another compatible pen by sliding off the gripping section. One small caveat: the original Diamond 530 nib is slimmer in profile to the later Bock and JoWo units. This means that if you have one of these pens then a new nib may not fit in the inner cap. If you encounter this problem, we can supply a new wider inner cap. All the nibs come in holder case for storage when not in use.
TWSBI's Diamond mini uses a smaller number 5 size nib to that on the Diamond 580. The feeds and collars look the same as those on the Diamond 580 but they are in fact subtly different.
The Classic model uses the same nib, feed and collar as the Vac mini. Therefore, nib assemblies can be interchanged between TWSBI Classic and TWSBI Vac mini pens by removing the front section parts.
Although the Classic model uses the same nib and feed as the Diamond mini, the collar is different so Diamond mini and Classic nibs are not fully interchangeable. If you want to fit a Diamond mini nib to a Classic, the nib has to be removed from the collar together with the feed. This task is quite difficult and can often result in damage to the feed.
The TWSBI Vac mini uses the same nib/feed/collar assembly as the Classic but mounted in a different front section. Luckily, as of October 2016 TWSBI produces spare nib units for the Vac mini range.
Vac 700 and Vac 700R
The TWSBI Vac 700 model uses a larger number 6 size nib (manufactured by JoWo) so is completely incompatible with other TWSBI fountain pens. Larger Edison pens use the exact same nib as do models from many other manufacturers. The Vac 700R now replaces the Vac 700 model and has an improved shut off value. The 700 and the 700R nib units are not compatible although they look the same.
Early Vac 700 models used a Bock nib. These can be identified by the point size label (F, M etc) being on the side of the nib body rather than the top as is the case for the Jowo nibs.
TWSBI Vac 700 and 700R nib assembly
TWSBI Micarta pens (now discontinued) use the same nib as the Vac 700 models but the nib is gold plated. Mark 1 pens had a Bock nib with Mark 2 models featuring a JoWo nib. Please refer to the notes in the Vac 700 section above regarding identification.
Eco and Eco T
The TWSBI Eco uses the same nib and feed as the Diamond mini, Classic and Vac Mini models. However, there is no interchangeable assembly like the Diamond mini so the nib and feed have to be pulled out of the body of the pen. Although the Eco models use the same nib and feed as the Diamond mini, the Eco does not have a collar like the Diamond mini so the nibs are not fully interchangeable. If you want to fit a Diamond mini nib to a Eco or Eco T, the nib has to be removed from the collar together with the feed. This task is quite difficult and can often result in damage to the feed.
TWSBI writing samples
Writing samples are 300 DPI and the paper is 8mm spacing
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