Can anyone describe the writing characteristics I might expect from a Signature 4 nib? I just picked up a 'J' that needs a new sac and it is fitted with this nib. Is it F/M/B/stiff/etc.?

Sounds like an aftermarket replacement nib, or something someone threw in there when their Esterbrook nib went bad. Hard to say what it'll write like without actually inking it up.

Best-
Brian

I resacced the "J" and the "Signature 4" writes a smooth, wet medium line. The nib is smaller than my 9556 nib and it is gold colored but unlabelled in regards to plated/solid gold.
Oddly, when I put my the 9556 in this pen, the cap rubs on the nib due to the nib's wideness. Any idea why?

(cap rubs against nib)

I had a similar issue with my 9312 and one of my SJs but it has since gone away.

William

I might try to gently bore out the inside of the cap so it accomodates the standard 9xxx nibs using a drill.

That should work, although I would be wondering why it rubs. Perhaps the inner cap isn't fully inserted in the cap (although it should be pushed in by the shoulder of the section itself). The 'J's were all made to accommodate all nibs, so interference is uncommon. Might even be a replacement inner cap...

Well, careful enlargement by boring a bit outwon't hurt, and a replacement inner cap is relatively easy to obtain should you have a problem...

Regards,

Gerry

As for plated or solid, try passing a magnet over the nib (a fridge magnet should do) if it attracts than you can be pretty sure you have a plated steel nib

I wrapped a narrow chopstick in sandpaper and widened the inner cap. All is good now.