What's slightly bigger than an 8-32 thread?

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Frank O

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Strictly speaking I suppose this isn't machining per se, but I'm sure there have to be people here who can answer my question.

I have a piece of gear made in the U.S. probably in the 1950s, which has several threaded posts for electrical connections. There's a corresponding nut on one of the posts, but the remaining posts lost theirs.

I took the remaining nut to the hardware store and tried it on their test threads. It seemed to be a good fit for 8-32, so I bought a packet of those and brought them home. However, when I tried to put one of the new nuts on the device's posts, they wouldn't fit.

So, is there a thread size slightly larger than 8-32 that's a good candidate to be the one I need? Close enough to 8-32 that I might have thought it was a fit? I seriously doubt this is metric, due to the vintage.
 
Do you have a micrometer and a thread gauge?
What is the OD of the thread on the stud?
What is the thread pitch (TPI) on the stud?
Those are the questions you need to answer.
The thread in question may not be a current UNC or UNF. It might be an obsolete standard or even proprietary.

To answer the question you asked: there are many threads "slightly larger" than 8-32, depending on what one considers "slightly".
Slightly is not a well defined unit of measure.
 
Machinery's Handbook shows a "fine thread" 8-36, which uses the same #29 drill, so would probably be pretty hard to tell apart from an 8-32. The wrong thread would certainly make it hard to screw a nut on there.
 
8-36 max diameters are "slightly larger" than 8-32 max diameters.

Tom
 
Meterc?

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Did you consider that it may actually be an 8-32 and the ends of the threaded studs you are trying to put the new nuts onto may have been peened to retain the original nuts? That was (and still is) pretty common with electrical fittings and the stud ends being a bit buggered make putting new nuts on a bit of a challenge. But it certainly can be done -

Another shot in the dark - YMMV

Stu
 
It may be a 9-32 thread. I have never seen one but I have had the same problem with 5-40 vs. 4-40 threads. A 9-32 nut would fit an 8-32 screw (loosely). Many of the electrical studs that I have run across are 10-32 but that would be a very loose fit on an 8-32 screw. 9-32 is definitely not a standard size.
edit: strike erroneous link
 
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I suspect 8-36 as well
Another bit of trivia: It's a very close match to metric 4mm also
 
gr8legs said:
Did you consider that it may actually be an 8-32 and the ends of the threaded studs you are trying to put the new nuts onto may have been peened to retain the original nuts? That was (and still is) pretty common with electrical fittings and the stud ends being a bit buggered make putting new nuts on a bit of a challenge. But it certainly can be done -

Another shot in the dark - YMMV

Stu
Click to expand...
If the old nut felt snug as you were removing it this would be the most likely reason your new nuts feel like they don't fit don't fit. Best thing you can do is measure the diameter of your studs down close to their base, past where they would be peened.
 
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