Above is an example that’s easier to see: two sides of a Kaweco Sport double-broad nib. On the left is the normal tipping material, which is nice and thick. On the right is the reverse side of the nib, which has a smaller profile, but still has recognizable tipping.
There isn’t always enough tipping material on the reverse side, or sometimes it’s too scratchy. But it’s worth trying in a pinch. On the Kaweco AL-Sport extra-fine nib, for example, the reverse side is quite nice. It just needed a few light passes with micromesh to be silky smooth, which is great for an extra-extra fine.
Here are some writing samples to show the difference between the two sides of a few nibs. First is the Kaweco extra-fine. The first three lines are written with the normal extra-fine tip, and the next are written with the reverse.
You can see that the reverse really gives a nice, thin line. I just used this to fill out a sports team form release, to make sure all the information was legible.
Using the flip side of the nib also works with wider nibs. Here is a Montblanc broad. The Montblanc’s reverse side isn’t as smooth as the Kaweco reverse side, but it still writes more narrowly.
Here is a vintage Parker Vacumatic.
So, it’s a nice little trick. If you need a thinner line and don’t want to pull out a different pen, turn the nib over and see if that works.