What's the best way to determine a small inside hole thread pitch?

[Chipper5783]

Make up a small “hook” gauge. Just a small scrap of wire, pointed at one end, then bent into a tight hook (so it will fit in the hole). Then go across as many threads as you can, dragging the hook across the threads and count how many threads - measure how long the tail of your little wire gauge is from start to finish. Then take # of threads / change in protrusion of the wire to get threads per inch. You can practice on a hole that has a known thread pitch in it. It has to come out close to an integer value, if it doesn’t then perhaps it is a metric thread. Of course the more threads (longer distance) you can go over, the better.

Unless it is a very old, or really unique component, it should line up to some sort of chart value (a UNC, UNF, pipe, metric standard).

 

[Ulma Doctor]

If you are going to block it off, drill and tap for whatever size you need.
if you use a pipe tap, you can use pipe plugs

 

[extropic]

The first questions I would ask are regarding the Country of Origin and function of the equipment needing repair. In this day and age of global sourcing, I think it's too much of a stretch to assume NPT fittings. If the equipment is good old USA manufacture from 50 years ago, maybe NPT can be a reasonable bet. However, if it's 5 year old and from India or SE Asia, the options are much wider.
The link below may help explain some of the differences between NPT and BSP threads.

NPT vs BSP: Differences, Chart, NPS, BSPT - Plumbing Sniper

I was writing an article about the different types of thread sealants and I remembered that all threads are not created equal. Pipe thread forms in the United States is different to that of the United Kingdom. The two main types of pipe thread styles are National Pipe Thread (NPT) and British...

plumbingsniper.com

 

[RaisedByWolves]

I have a small brass gas valve that had a schrader valve (looks to be different threading on both sides) that was broken off by careless handling. Threads on the external broken off piece measure 5/16" by 32 (unbroken side).

The blind hole seems to measure 28 TPI - and I can't find a bolt that matches this threading (I am deleting the valve as it is no longer used and is a potential source of leaks) as I am blocking this off.

What's the best way to determine the inside hole thread pitch?

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Until I saw the side view I was thinking 1/8” npt.

Still, maybe.

 

[Lathe_Bender]

@extrop, the part has all the markings removed. The manufacturer is all about trade secrets and patent enforcement. They don't sell individual parts, only complete units. If you want a part repaired or replaced, the entire unit (and unit means the entire whole machine) has to be sent back to the manufacturer for a "flat rate" repair.

I'm going to try some saran wrapped in a small tube shape, placed in the hole, and mash JB Weld putty into the hole. Once it hardens, I should be able to remove my JB Weld "prototype" and take measurements so I can find out what I need.

What do you guys think about that idea - any pitfalls?

 

[Ulma Doctor]

It's probably 1/16 pipe. Readily available online but can be hard to source locally. Most home centers don't carry smaller than 1/8 but if you have a local hydraulic supply they may be a possibility.

I concur

 

[Ulma Doctor]

@extrop, the part has all the markings removed. The manufacturer is all about trade secrets and patent enforcement. They don't sell individual parts, only complete units. If you want a part repaired or replaced, the entire unit (and unit means the entire whole machine) has to be sent back to the manufacturer for a "flat rate" repair.

I'm going to try some saran wrapped in a small tube shape, placed in the hole, and mash JB Weld putty into the hole. Once it hardens, I should be able to remove my JB Weld "prototype" and take measurements so I can find out what I need.

What do you guys think about that idea - any pitfalls?

You could try to use a some plumbers putty to make an impression if you were so inclined

 

[extropic]

@extrop, the part has all the markings removed. The manufacturer is all about trade secrets and patent enforcement. They don't sell individual parts, only complete units. If you want a part repaired or replaced, the entire unit (and unit means the entire whole machine) has to be sent back to the manufacturer for a "flat rate" repair.

I'm going to try some saran wrapped in a small tube shape, placed in the hole, and mash JB Weld putty into the hole. Once it hardens, I should be able to remove my JB Weld "prototype" and take measurements so I can find out what I need.

What do you guys think about that idea - any pitfalls?

Well, you have continued to avoid disclosing what the equipment is, it's country of origin and it's vintage. Congratulations.

Because your stated intention is to plug the hole, why not just plug it with JB weld? I get the impression you are familiar with that product line.

If you insist on making a JB Weld "prototype", I suggest you include an Allen key to facilitate removal.

 

[Lathe_Bender]

@extropic
"Well, you have continued to avoid disclosing what the equipment is, it's country of origin and it's vintage. Congratulations.
No worries on that! It's an old mosquito magnet, designed in USA, made in China, and ti's around 10 years old.

Because your stated intention is to plug the hole, why not just plug it with JB weld?
I could, but I'm not familiar enough with the product to understand how it expands and contracts compared to the brass itself.

I get the impression you are familiar with that product line.
Only because an "auto mechanic" used it to "repair" an intake manifold bolt he had broken off and didn't want to properly extract. Ruined my car's head gasket due to air bubbles entrained in the coolant due to the poorly installed intake manifold.

If you insist on making a JB Weld "prototype", I suggest you include an Allen key to facilitate removal.
That's a good thought!

Because I'm not wanting to go to Walmart and find the JB Weld, I ordered some 1/16" and 1/8" NPT fittings from Amazon. They should be here tomorrow and I'll see what fits.

 

[Lathe_Bender]

In case you were interested in what I'm trying to fix:

Similar Patent:

U.S. Patent for Attractant system for mounting to an insect trapping apparatus Patent (Patent # 7,293,387 issued November 13, 2007) - Justia Patents Search

The present invention relates to an attractant system for mounting to an insect trapping apparatus.

patents.justia.com

Similar Device:

Mosquito Magnet® Patriot Plus Mosquito Trap

With the Mosquito Magnet® Patriot Plus, you can establish a defense zone for your home or business that drastically cuts back on the breeding population of biting insects.

www.mosquitomagnet.com