How can I add friction to the threads of a fountain pen cap?

[Wilbur]

A few of my vintage pens have worn threads and the cap unscrews itself while in my pocket.  I have tried wax on the theads, which sometimes works.  Is there another solution besides swabbing the threads with crazy glue?  Thanks for the help.

[Ron Z]

No.  Please don't do that.  I've seen people use superglue and  stuff like it to "fix" a pen.  One recent one resulted in the grip knob of a pen getting permanently glued into the cap, a Pelikan section that didn't quite get back on the barrel, resulting in a big gap and the glue displaced gluing the nib unit into the barrel.   The repair was difficult and expensive.

 

You don't say what the pen is, and the approach can be different depending on the pen.  Sometimes swapping caps takes care of the problem.  What we often do is to stretch the barrel so that the cap engages the barrel threads again.  Done right you often can't see the repair.  But it's tricky work, and if you aren't careful you can ruin a pen.

[Wilbur]

Thanks for the reply Ron.  

You prompted me to do more experimentation.  The pen in use with the sloppy-fit cap is an Esterbrook J.  I have tried the cap swap:

1) five other caps thread onto the sloppy-fit barrel well and stay on;

2) the other pen barrels fit the sloppy-fit cap a bit looser and have the same tendency to pop loose;

So the cap seems to be the faulty part. 

 

Another pen is a Conway Stewart.  I have no others of those and the cap comes off "at the drop of a hat," so it's not trustworthy to carry.  No big deal, it's a desk pen.  Your idea to enlarge the barrel in a safe manner is interesting. 

[Wilbur]

PS Ron,

I have applied heat in the wrong manner and made a small warp much worse on a pen.  It was unnerving to watch it shrivel in the span of a second, like a hot dog left on the grill too long.  One has to learn somehow, but the supply of vintage pens is limited!  Luckily some damage can be undone, but now I'm thinking of another pen that I had to reheat and untwist.  Brutal, are we so-called pen restorers.  That's why I asked for help on this problem.

Best regards,

Wilbur

[VacNut]

There already are discussions on this method of stretching the barrel. The older method of restoration was to cut off a short section of the barrel threads, so the cap engages another barrel thread.

 

I do not know if an Etsy Section is threaded into the barrel or shellac.

If threaded you have to use a mandrel that matches the threads of the barrel so that the barrel threads do not get flattened with the stretching.

 

It is not an easy process, but it could be a great experiment for the DIY. Just be careful as an Etsy barrel is relatively thin.

 

How about that replacement cap…

 

 

[Wilbur]

VacNut, thanks for the information.  Here's a little back to you in return.

It's interesting that the vintage Etsy section fits the barrel with no threads or shellac.  The neck of the barrel is thin and it stretches over the rear of the shaped fitment and becomes nice and snug when fully engaged.

If that beautifully engineered fit becomes loose, say the barrel cracks a little at the mouth, the section can be glued on with shellac. 

 

[Claes]

A non-destructive "remedy" could be to wrap a piece of plumber's tape around the barrel thread.

It probably will look ugly, but as a temporary solution...?

 

Have fun!
Claes in Lund, Sweden

 

[VacNut]

2 hours ago, Wilbur said:

VacNut, thanks for the information.  Here's a little back to you in return.

It's interesting that the vintage Etsy section fits the barrel with no threads or shellac.  The neck of the barrel is thin and it stretches over the rear of the shaped fitment and becomes nice and snug when fully engaged.

If that beautifully engineered fit becomes loose, say the barrel cracks a little at the mouth, the section can be glued on with shellac. 

 

I believe Etsy sold nibs and the “pen” was just considered the holder. 
I don’t know about the quality of engineering on the Etsy as a bent barrel from heat is very uncommon in other higher priced pens.

No worries, there are thousands of replacement parts available. Let us know how your experiment goes.

 

You can search this forum on the use of plumbers tape to fix threads.

 

[FarmBoy]

Please don’t shellac in sections. 

[Wilbur]

Farmboy,

What do you use instead of shellac to join sections to the barrel? 

W.

[FarmBoy]

Section Sealant.

[BigJess]

Is section sealant the same as thread sealant? I asked the googler and couldn’t find a reference to section sealer. 

[Paul-in-SF]

On 3/30/2025 at 8:49 AM, Claes said:

A non-destructive "remedy" could be to wrap a piece of plumber's tape around the barrel thread.

It probably will look ugly, but as a temporary solution...?

 

Have fun!
Claes in Lund, Sweden

 

 

I did this once on a pen ("plumber's tape" being ultra-thin teflon tape used as a thread sealant in plumbing) but I carefully, with tweezers, applied it inside the cap, so it was not easily visible (you can do this a small piece at a time, a little overlap doesn't seem to matter). The first time you screw the cap on the barrel, it sets the tape into the threads, making them slightly tighter. It does seem this is reversible if needed, and effective in sealing the inside of the cap better than it was before. The tape sticks to the cap threads but not the barrel threads, I'm not sure why. I did use a cotton swab to push the tape as much as I could onto the cap threads before the first time I threaded the barrel. 

[Wilbur]

Big Jess, 

I think section sealant is the goo that is made from heating pine rosin with castor oil.  It is sticky and seals threaded section/barrel joints against ink leakage.  If you want to take it apart, it softens with not too much heat.  But I could be mistaken in exactly what Farm Boy meant...

 

Paul,

Teflon tape inside the cap threads is worth a try!  Thank you.