The TWSBI Diamond 540 has been a phenomenally popular pen, and for good reason: it’s the cheapest piston filling fountain pen of decent quality currently available. Well, at least if you know where to look. That problem’s due to TWSBI phasing out the 540 for the new 580 that will bring a few design improvements.
As seen in the image below, there are several noticeable differences between the 540 and 580. The first is the shape of the clip. We’ve already seen this on the Mini and the Micarta. Personally, I prefer the look of the one currently on the 540, but whatever.
One subtle change is the use of thicker o-rings in the piston seal. I haven’t heard of this being an issue so I’m a bit curious as to why the change.
The other three changes pointed out in the image all strive to resolve cracking issues. There’s now a metal sleeve in the front of the section that the nib unit friction fits into. Previously, there were several ribs around the nib unit designed to help align the unit and the section. A major cause for cracking the section came when people removed the nib unit and tried to reinsert it without lining up those ribs with their intended slots in the section. This new metal sleeve should definitely resolve that.
Looking towards the rear of the pen we can see the metal collar in the the barrel of the 540 has been removed and the piston unit now threads directly into the barrel. Also of note is the metal ring at the rear of 580’s barrel. I don’t know the exact purpose of that ring and my inquiry went unanswered so I’ll have to speculate. Many would be ecstatic, myself included, if this was intended for the cap to post to. It’s a similar design as currently used on the Vac700. But, I don’t think that’s the case. If you post the 540 you’ll see that the cap posts onto the piston knob and the lip of the cap would have to move several millimeters to get to the point where the metal ring is. TWSBI would have had to completely change the dimensions of the rear of the pen, the inside of the cap or both to get this to work. I’d be surprised if TWSBI made such a significant change as Jim (Speedy) has said before that he never intended people to use the pen in the posted position.
One thing’s for certain: I can’t wait to get my hands on one!