10-32 versus M5???

[rwm]

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

 

[rwm]

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

 

[sdelivery]

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???

5mm!?!

 

[wayback machine]

Speaking of thread engagement -
I read somewhere, that all or most of the strength or load capacity of any threaded fastener is in the first 6 threads, no matter how long the bolt is.
Is this true? Or not?

 

[Mitch Alsup]

Speaking of thread engagement -
I read somewhere, that all or most of the strength or load capacity of any threaded fastener is in the first 6 threads, no matter how long the bolt is.
Is this true? Or not?

Yes, and it is a direct consequence of Young's modulus (of steel.)

A properly torqued threaded fastener transmits <almost> all of the force (96%+) through the first 5-6 threads as stretch in the fastener and threading of the nut.

It is also a reason you want to chamfer the face of the thread, and why some threaded parts have thinner non-threaded shafts, and why all high torque fasteners have chamfers and fillets.

....

 

[Parlo]

A nice feature of metric socket cap head screws is their proportionally larger head diameters allowing for bigger clearance holes if required.
For example:
10-32 head diameter 7.9mm - M5 head dia 8.5mm.
5/16" head diameter 11.9mm - M8 head diameter 13mm.

 

[Jeff.64]

When mixing inch and metric can't be avoided, I use the blue dyed metric screws where possible.

McMaster-Carr

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www.mcmaster.com

 

[rwm]

Clever! I didn't know they existed.

 

[j-becker]

Yes, and it is a direct consequence of Young's modulus (of steel.)

A properly torqued threaded fastener transmits <almost> all of the force (96%+) through the first 5-6 threads as stretch in the fastener and threading of the nut.

It is also a reason you want to chamfer the face of the thread, and why some threaded parts have thinner non-threaded shafts, and why all high torque fasteners have chamfers and fillets.

....

close to 80% of the load is born by the first three threads even if you have more threads engaged using steel fasteners in steel. You can design nuts to have a more even load carrying ability. For practical questions NASA has some nice data: https://ntrs.nasa.gov/citations/20170003491

 

[ChazzC]

A nice feature of metric socket cap head screws is their proportionally larger head diameters allowing for bigger clearance holes if required.
For example:
10-32 head diameter 7.9mm - M5 head dia 8.5mm.
5/16" head diameter 11.9mm - M8 head diameter 13mm.

I’ve found that there is a greater selection of metric washer OD’s (both larger & smaller than inch/Imperial/English); I regularly use 5mm washers on 10-32 fasteners.