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10-32 vs 10-24 Just curious why 10-32 is more popular when NC is more common.

Funny that 10-32 and M5 interchangeability comes up. I have made a living copying OEM parts and selling them for less. 15 or 16 years ago we started making these parts.Z-RodIMGP2853.jpg
Measured a bunch of competitors parts and OEM parts and decided they threads were 10-32 3A as they would not go into a 2A gauge. Made them for about 12 years before I found out they were supposed to be M5 on the loose side. Had about 500 blank screws on hand and decided to use them up before making them right the next time. I did mill the threads and made them drag in the 3A gauge.

CalG and I had a discussion about loose threads being accurate in concentricity checking. Turns out the engineers that designed this assembly were correct. The loose threads contributed to the .0005 TIR needed for them.

Threading a barrel, accuracy
I thought by now someone who is worried about social security would have provided the answer. Before CNC machines there were screw machines. 6-32, 8-32 & 10-32 - just change a couple slide cams, the die and throw in the correct stock size. No need to reset the pitch feed. Any beginning apprentice in the shop could change over with ease. BTW - screws machines can make other turned parts. I used to engineer eye-wash valves to be turned on a screw machine.

Include the fact the electricians trade preferred a 32 pitch for the thin wall they worked with - you now have a built in customer base.
From reading the old literature, I thnk that the basic reason was the materials of the day. The original coarse threads were optimized for cast iron, and the fine threads were optimized for mild steel. The finer threads also clamp more tightly and are less likely to come loose in use. Metric threads, which arrived far later, merged coarse and fine, tending toward the fine. But there are coarse metric threads as well - a later addition?
Pardon me for going a little off-topic here but does anybody know of a source for 10-30 screws? I need one for this ancient Rockwell hardness tester.


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In some places, 10-24 machine screws are still called 3/16 stove bolts.

Stove Bolts - Fastener Mart


And, just to add to the mix, I had to make a 10-36 shoulder bolt and tee nut last month. They were Hardinge Brothers' choice of threads in their circa 1910 Cataract bench lathe screw cutting attachment. No, I could not substitute 10-32. The shoulder bolt had to fit an original tapped hole and the tee nut had to fit an original screw.

Went thru misc taps & dies- Got a 10-36!

and 2or3 3/16! Chart says drill size was dif from 10 or 12, so I made a place for them on my new board. I get that wrong?

Also some odd pitch 1/4- don't remember, so there's FOUR places for 1/4.
and an 11/16-18.
Come in as handy as the straight eight head gasket hanging on the wall
Most of the Home Depots I go to do have 10-32 but you have to dig for them in there is a limited selection.

As for the original question the 32 tpi do have greater holding strength in thin and or soft materials, also don't strip out as easy in soft alloys.

10-24 are usually used with nuts whereas 10-32 are often threaded into thin sections such as the green 10-32 grounding screws used in outlet boxes.
Could those holes have had either Helicoils or other inserts?

There are specs for "aircraft grade" 10-24 bolts and the like, but those were mostly used in older piston aircraft.
We build a lot of aluminum hydraulic parts for aircraft, everything from two seaters up to the biggest wide bodies. Just about everything that has to hold any kind of pressure uses some type of thread insert, Heli-coils are the most common, but we see Keensert type inserts occasionally.

While we are on the subject, these are the machine screw sizes that we see most commonly in this type of work:
I don't know why they switch to the fine threads at 10-32 & 12-28, but this is pretty common. I've been doing this kind of work for 25 years and only seen 10-24 or 12-24 a handful of times, I see sizes 2-8 in the fine pitch maybe about 10% of the time.
Funny that 3-56 is not more popular. It has about 80%-gauge equivalency with a metric thread. 2.5mm I think. I make another part that I used 3-56 on the threads because the gauges were a few dollars cheaper. Then a customer specified the metric equivalent on a similar part, so I bought the metric plug gauge anyway. Almost saved some money.
The helix angle gets quite steep on course threads in small diameters. The root diameter suffers as well, so 24s tend to twist off too easy. Like said thinner mat. works better with fine thd. ( number of threads engaged).
The English 2BA thread is interchangeable with 10-32 and M5 from what I remember 40 years ago working at my dads shop

For the purpose of consumer products and goods, M5 and 10-32 interchange.

The guys commenting in this thread that premium SHCS and nuts do not and Formula one fasteners and NASA fasteners do not have missed the point.

Buy a box of M5 Phillips heads and no grade 10-32 nuts from Lowes or Mcmasters or anybody. They fit perfectly together.

Tap a 10-32 hole and an M5 in 10awg aluminum and try a 10-32 and an M5 Phillips screw in each. They both work same.

Like I stated before, major worldwide autoparts manufacturer uses m5 and 10-32 interchangeably. For a fact.

I'm sure NASA, Formula 1 and other places use high end fasteners made to the proper specs.

Mass produced consumer screws, not so much.
I’ve definitely had #10-32 screws strip without reaching acceptable torque loads in what turned out to be an M5 application. Sometimes you get lucky, and sometimes you wonder why a screw won’t stay tight.
10-32 and M5x.8 are the same thing, interchangeable for most applications.
The difference in pitch is negligible, the difference in diameter not always. You can always put a 10-32 screw in an M5 tapped hole, you can't always put an M5 screw in a 10-32 tapped hole. Works out well here in the U.S. where 10-32 screws are much more common.
I was told by an old engineer that NC threads were exclusively used on aircraft. He meant piston-engine, and maybe military, I guess. I have no info of my own on this, but it did seem curious because of course the larger root diam on NC makes the screw stronger.
IF his assertion is true, the one reason I can see is that coarser threads are more tolerant of dirt and damage. A ding on a fine thread will cause more trouble than the same-size ding on a coarse. 0.001" oversize in a hole before tapping reduces thread engagement % by more for a fine than for a coarse thread. This has to be the reason for the preference for coarse threads into soft castings, because the fine thread has larger calculated shear area than the coarse.
I haven't read all the posts, so forgive me if someone has already said this .
In my experience, the 10-32 isn't always used for a fastener.
In some instances ( guns, sewing machines, etc) they use a set screw that is fine thread for adjustments . Adjusting a sight, travel in something, etc.

In electronics , if it's a real shallow hole it would allow for more thread engagement. Not much, but maybe 1 more thread.