Odd nipple

[airiest-falcon0n]

I’m cleaning up an old Spanish-made, back-action, .28 ga. “Monkey gun” my dad brought us back in the mid-60’s. We shot the heck out of it, until we ran out of powder & caps. Amazingly, there was no rust or corrosion anywhere on or in the smoothbore barrel. Now to my question-what size nipple does it take?
I assume metric, but my thread pitch gauge has a weird tip that makes it nearly impossible to measure the very few threads available. The o.d. of threads is 5.1mm/.20”. Existing nipple is a little peened, but useable. I’m hoping to find a spare, as opposed to drilling/tapping it. My track record of retapping anything that I couldn’t square up to the drill press is not very comforting. Any ideas?
At 73 yrs. old, I’m not likely to wear this original nipple out, but I’m thinking to the future…

 

[bpd303]

Any decent hardware store will have both metric and US thread gauges. I would take the nipple there and try it in their gauges. Once you have the correct thread go to Track of the Wolf and order the right nipple. If the nipple is just a little peened/mushroomed clamp it in a drill and run the drill while lightly filing the nipple until the caps fit snugly. I always put a little anti seize on the threads when installing the nipples.
Would love to see a couple of pictures of the gun.

 

[Notchy Bob]

A #12 machine screw would be pretty close to that diameter, and some revolvers, such as the Ruger Old Army, I believe, used nipples of that diameter. Track of the Wolf has a tremendous selection of nipples, something like four pages. Some of them are intentionally made oversized for wallowed-out threads, although I have not checked to see if they have any with oversized #12 threads. You might try browsing through those pages just to discover what options are available.

I would second @bpd303 ’s suggestion, however. I think it’s a good idea to ascertain the actual size and thread pitch with a proper gauge. The little folding thread pitch gauges with the toothed blades are handy, but the results you get with these are not always unequivocal, especially for those of us with deteriorating visual acuity. Some hardware stores have thread gauges and some don’t. I bought a fractional “Screw Checker” plate from Brownell’s many years ago, and maybe two years ago finally broke down and bought small and large metric Screw Checkers to match, from Victor Machine Tools. These have proven to be invaluable when puttering with muzzleloaders, and they are not expensive. You can tell by feel when you have the right thread.

Good luck with your project!

Notchy Bob

 

[bpd303]

the actual size and thread pitch with a proper gauge.

The hardware store where I do most of my shopping, has the thread gauges that you actually thread your sample into it gives the size and pitch.