Difference between M5 and 10-32 UNF? (2024)

One of my co-workers is telling me that M5 x 0.8 Male and 10-32 UNF Male are exactly the same and that we can carry one model for both applications. But I'm not so comfortable with it unless I know for sure. Tried looking a bit on line but I'm not overly familiar with these thread types. Any hints/suggestions on where to research would be most appreciated.

In case you're wondering its not for screws / fasteners its for push to connect fittings

*Follow up*

Wow thank you all for the responses, moving I'll continue to stock both and ask that they use the correct thread for the correct application and that no creative swapping is to be done.

A 10-32 screw will go in a M5 hole, but it's sloppy. An M5 does not go in a 10-32.

Definitely not the same. I had an employee once who used a 10-32 to set a bunch of M5 rivnuts. When the parts went to assembly they couldn't install the fasteners.

I reworked them by running an M5 form tap through each one and pushed the threads back in place.

KennyPowers said:

One of my co-workers is telling me that M5 x 0.8 Male and 10-32 UNF Male are exactly the same

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One of your co-workers is an idiot.

10-32 UNF Class 2B
Major OD - 0.1831" - 0.1891"
Pitch OD - 0.1658" - .1688"
0.03125" between threads

M5 x 0.8 Class 6g
Major OD - 0.1900" - 0.1959"
Pitch OD - 0.1717" - 0.1754"
0.03150" between Threads

As others have mentioned, the TPI is almost identical, so the threads will engage as long as the screw can fit in the hole. But the M5 fastener is almost 4% larger than the 10-32, which is enough to cause interference in most fits.

KennyPowers said:

One of my co-workers is telling me that M5 x 0.8 Male and 10-32 UNF Male are exactly the same and that we can carry one model for both applications. But I'm not so comfortable with it unless I know for sure. Tried looking a bit on line but I'm not overly familiar with these thread types. Any hints/suggestions on where to research would be most appreciated.

In case you're wondering its not for screws / fasteners its for push to connect fittings

*Follow up*

Wow thank you all for the responses, moving I'll continue to stock both and ask that they use the correct thread for the correct application and that no creative swapping is to be done.

Click to expand...

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they are not the same but i have seen mistake where thousands of 10-32 used when should have been M5 screws. when after months a large operating machine had random screws loosen up and cause problems it was discovered the error. screws were replaced and random screw loosening stopped happening.
......under lightly loaded condition it might go unnoticed by why would you use inch screw for metric threaded holes ?

This is about push fit hose conectors, they have at most 1d of thread length and thats hollow, they wind in just fine in any of the combinations, the oring on the bottom of them seals the thread and the push fit fitting bits seal the hose. Normally were most people go wrong is they over torque them and snap em off. the slight thread differences won't matter here, equally they wont vibrate lose as the rubber ring works as a great thread locking device.

DMF_TomB said:

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they are not the same but i have seen mistake where thousands of 10-32 used when should have been M5 screws. when after months a large operating machine had random screws loosen up and cause problems it was discovered the error. screws were replaced and random screw loosening stopped happening.
......under lightly loaded condition it might go unnoticed by why would you use inch screw for metric threaded holes ?

Click to expand...

British Airways flight 5390 had its co*ckpit window blow off and a pilot was sucked halfway out the window during flight (he lived and went back to flying!) when a mechanic replaced a window and used the screws that someone else had used before. The problem was that some were #8 UNC and not #10 UNF. and that others, while #10 UNF, were 0.7 inches long and not 0.8. The investigation showed that the feel of the #8 screw stripping was about the same feel as the torque screwdriver clutch indicating proper torque. This was compounded by the torque screwdriver having a problem with grease breakdown. The mfr had actually changed lubricant specs becuase of the problem, and the actual torque screwdriver used was tested and was found 1) to have been set improperly and 2) to not release at the proper set torque.

In critical applications, I think I'd completely ban other the 5mm or the #10 screws from the shop. One or the other. Just too easy to f up.

You talk about a "perfect storm" of screwups:
Mishap: British Airways Flight 539