# 10-32 versus M5???



## rwm (Feb 1, 2021)

I learned something amazing today that I probably should have known years ago. Perhaps all y'all already know this but I will enlighten those who do not.

A 10-32 and and M5 coarse screw are almost identical! I mean so close that I cannot always tell them apart with a caliper and a thread gauge. Depending on the thread class they may even mate with the incorrect opposite and work just fine.
After some research I have determined the following:
The major dimeter of a 10-32 is 0.183 to 0.189". The major diameter of an M5 typically measures near this range or minimally larger. My stock is 0.190!
The pitch of a 10-32 in mm is .794mm. The pitch of a M5 coarse is .800. These are too close to see visually. If you engage a metric screw in a 10-32 socket it will make multiple revolutions before binding. For a short thread like a nut you may not even notice.
Also, the socket on my 10-32 cap screws accept a 4mm hex key perfectly!
As far as I know, other sizes are not nearly this close and never interchangeable.

*M5 and a 10-32*



Don't mix up your stock!
Robert


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## rwm (Feb 1, 2021)

After some experimentation, all of my 10-32 screws will thread into M5 nuts and don't feel too sloppy. Only some of my M5 screws (with smaller ODs) will fit in my 10-32 nuts.
Robert


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## brino (Feb 1, 2021)

I stumbled over another one lately on small set-screws; #5-44 is so very close to M3x0.5 I could not tell them apart.
I could make them both thread into both a metric and imperial thread checker!

I have been meaning to make up an excel chart of the common imperial and metric fasteners with both diameter and pitch columns and then come up with a formula in another column to represent how close of match they are. I think having that would help me in the shop when I am trying to determine an unknown thread.

-brino


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## markba633csi (Feb 1, 2021)

There's another one: 8-36 and I believe 4mm or 4.5 can't remember which. Nearly identical. The 8-36 is just a hair fatter IIRC
-M


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## mattthemuppet2 (Feb 1, 2021)

yeah, they're almost the same but they're not. I usually find out I've got one in the wrong draw because it either won't thread into a matching nut (M5 screw, 10-32 nut) or the nut is so loose that it feels like it's going to fall off (10-32 screw, M5 nut). It's a real bugger to sort them by eye.


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## rwm (Feb 1, 2021)

Any body ever run a M5 tap through a 10-32 hole to convert it? I may need to do that and I want to know how it will work out?
Robert


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## matthewsx (Feb 1, 2021)

That's a good reason to buy a package and not throw old ones into a drawer. If it was me I know I'd find one that didn't quite fit and bugger up the threads on something I cared about.

Yes, I have boxes of old hardware I use quite a bit but more and more I find myself just buying the right fastener for the job. Saves lots of headaches....

John


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## matthewsx (Feb 1, 2021)

rwm said:


> Any body ever run a M5 tap through a 10-32 hole to convert it? I may need to do that and I want to know how it will work out?
> Robert


It'll probably work


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## RJSakowski (Feb 1, 2021)

A 5/16-24 thread has an o.d. of .3125" and a pitch of .0416" and an M8-1.00mm has an o.d. of .3150" and a pitch of .0394"


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## Bi11Hudson (Feb 2, 2021)

Long(!) years ago, I was replacing Lucas (Prince of Darkness) electrical components on a motorcycle. I used Japanese, probably Suzuki, handlebar switches. Having "mislaid" the original screws, I scrounged around to find something to fit. As it happened, Nr 10-32 was tight but fit good. At the time, I didn't know metric vs imperial threads. But it worked and I stuck it in the back of my mind that some sizes were (almost?) interchangable. 5/16-24 vs 8mm is another I have run across helping with automotive work.

.


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## Braeden P (Feb 2, 2021)

i threaded a m5 to 10 32 just thought that it was a bad 10 32


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## Flyinfool (Feb 2, 2021)

Where I work we purchased a valve to use in a new piece of equipment. The spec sheet listed the mounting holes as M5 or 10-32. We used 10-32 and for many years of building this machine never had a field failure of the thread.


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## JPMacG (Feb 2, 2021)

I pulled a bag of used 10-32 titanium screws from a trash bin at work and used them to replace some steel M5 screws on my bicycle.  They worked perfectly and have been in use for many years.


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## Larry$ (Feb 2, 2021)

matthewsx said:


> That's a good reason to buy a package and not throw old ones into a drawer. If it was me I know I'd find one that didn't quite fit and bugger up the threads on something I cared about.
> 
> Yes, I have boxes of old hardware I use quite a bit but more and more I find myself just buying the right fastener for the job. Saves lots of headaches....
> 
> John


I settled on using metric for all new work. I bought assortment boxes from McMaster-Carr rather than the cheap Chinese stuff on eBay. The heads are all marked with their grade. Looking for the grade marking is also a good way to tell metric from Imperial. The McMaster hardware is quality & kind of expensive but has saved many trips to the hardware store. Buying a few screws at a time at the hardware store is expensive per piece. Eventually the sets will probably end up as cheap or cheaper on a per part basis and a lot cheaper in travel/time. When I run out of the most common sizes used I buy a package of 100 pc. from McMaster. 

I tear all sorts of old stuff apart to see how it works/was made. I save the hardware by product, until I'm really bored then sort. The pandemic has provided a lot of "bored!"


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## rwm (Feb 2, 2021)

matthewsx said:


> It'll probably work


Thanks John!
These are a series of screws that hold an elevator cable to the top of the car.
Robert


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## RJSakowski (Feb 2, 2021)

rwm said:


> Thanks John!
> These are a series of screws that hold an elevator cable to the top of the car.
> Robert


I hope that was tongue in cheek.  When fasteners with mismatched pitch are mated, there is full thread contact on only one thread.  While threaded fasteners do stretch under load so that the load isn't uniformly distributed to all the threads, aggregating the situation by purposely using mismatched pitches isn't wise.  For holding a nameplate on a machine, no problem.  Holding a elevator cable on a car???


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## rwm (Feb 2, 2021)




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## mattthemuppet2 (Feb 2, 2021)

i think it would be an elevator for mice if it used M5 screws to hold it up!


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## Bi11Hudson (Feb 2, 2021)

Maybe covers for the belts?


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## rwm (Feb 2, 2021)

It was a joke and I forgot to put the . These screws are intended to hold a light on my ebike.
Robert


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## rwm (Feb 10, 2021)

Case in point: I made a holder for the headlight on my ebike. Basically two shaft clamps with flats. I originally tapped the holes 10-32 without thinking. I then realized everything else on the bike was metric! I decided to re-tap the holes at M5. This seems to have worked out well. The threads look great to the naked eye and the screws torque down fine. I feel like this is acceptable for this application and will prevent a future problem when I mix up the screws.






Robert


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## rwm (Feb 26, 2021)

Here is a good example:
I needed to cut some internal threads in a part to mount a tail light on one of my bikes. The factory light has a base that is 25mm diameter threaded 1.0 mm pitch. This equates to 25.4 TPI pitch. Being inherently lazy, I did not want to change over my gears to metric. Also, that would eliminate my ability to disengage the half nut. The thread length is relatively short; about 1/4" of engagement. I decided to cut the threads as 26 TPI and see if that was close enough for this low stress connection.
In short, it worked like a charm. You would be hard pressed to tell that the threads were not congruent by examination or function.




Robert


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