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Indeed. The French measure their wheels (and consequent tire sizes) in thumbs, which happen to be inches.
Just remember, horses are measured in hands. Look at how far we've come.....

Indeed. The French measure their wheels (and consequent tire sizes) in thumbs, which happen to be inches.
That's the thumbest thing I've heard today!

Just remember, horses are measured in hands. Look at how far we've come.....
The "English System" should be renamed the "Caveman System" and maybe it'll encourage Americans to finally change.

Grog catch lizard almost foot long! Grog foot, not Monk foot.

The "English System" should be renamed the "Caveman System" and maybe it'll encourage Americans to finally change.

Are you serious? I'd totally get behind the "Caveman System."

Why or how did it end up combining Metric (width) with English (rim diameter)?
Same way our motors use mm for diameter and inches for length (although I have seen some places that have used mm for length). EX - C6-5 is 18mm diameter x 2.75" long

Seriously, the best information I have seen regarding the US of A and the Metric System.

His point about flying is still feet & knots based... Makes a certain consistent sense. If we accept 360 degrees for circumference, then sexagesimal division of degree, 60 minutes, then 60 seconds... One nautical mile is one second of latitude. Knots is just nautical miles per hour.

Miles of longitude varies by cosine of latitude, but otherwise it's easy to do the other navigation arithmetic in your head.

That was an important design consideration in pre-literate times, and for when paper and pencils are not available.

...
Has anyone flown a MiG? Do Russian and Chinese aircraft use feet and knots?

There are advantages to a system that uses human-scale units as well as units that are readily divisible into fractions.
Considering human-scale units, a whole degree Fahrenheit is about the threshold of what's noticeable for a temperature change, whereas a degree centigrade is so big (9/5 as big) that you're stuck adding a decimal place.
Considering divisible units, 12 inches in a foot is pretty handy. (But then for consistency we should really be using 12ths of an inch for small things, rather than 16ths, oof.) If only we had 12 fingers, our numbering system could be base 12, and then we could divide things into thirds as readily as halves. Hemingway cats FTW.
(Speaking of counting on your fingers, using binary you can actually count up to decimal 2^10 - 1 = 1023. Try it!)
Some calculators used to have gradians as an option for angle measurements, a right angle being 100 gradians. 400 gradians in a circle is kinda dumb though.
Then again, in imperial units, among the many ridiculousnesses is the conflation of mass with force. "Slugs," get outta here...

Conflation of mass with force only for the ignorant. The very word slug feels heavy.
I'm not sure my threshold of temperature perception is smaller than one degree C.
I have counted on my fingers to 1023, but it never became a habit. I think I'd probably move a finger by accident before I got all the way there.
Having been back and forth, not by my choice, I could wish everything was in metric, though it would take my intuition a while to come around. When I was a kid and I saw a few signs including kilometers, I would not have believed you if you'd told me we wouldn't make the transition by 2024.

Indeed.

So intuitive…

Years ago, I had a young engineer that worked for me, Smart guy but no real life experience. He came to me with a design for a 'small aircraft part' and it has 1/4-20 bolts on it. I'm looking at this thinking that he is really missing something in his design and analysis, 1/4-20 is a pretty big bolt for small aircraft parts. I told him that a bolt like that can hold a 'a few tons' in single shear. I could tell that a number like a few tons didn't register with him. At the time he drove a 80's Hyundai Excel, When I told him a 1/4-20 bolt could hold 'a couple of Hyundai's' suspended, his eyes got wide, and I could tell that he could think in terms of Hyundai's. He came back a few hours later replacing the 1/4-20 with a 8-32 screw. The unit of measurement of the Hyundai stuck.

Jump forward about 10 years, had an engineering intern. He was confused when he asked about a load on a part, and one of the engineers that worked for me told him 'a couple-a Hyundai's'.

Mike k

Want to fix a bigger problem? Find me the 1/4 inch on a 1/4-npt pipe thread.

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Years ago, I had a young engineer that worked for me, Smart guy but no real life experience. He came to me with a design for a 'small aircraft part' and it has 1/4-20 bolts on it. I'm looking at this thinking that he is really missing something in his design and analysis, 1/4-20 is a pretty big bolt for small aircraft parts. I told him that a bolt like that can hold a 'a few tons' in single shear. I could tell that a number like a few tons didn't register with him. At the time he drove a 80's Hyundai Excel, When I told him a 1/4-20 bolt could hold 'a couple of Hyundai's' suspended, his eyes got wide, and I could tell that he could think in terms of Hyundai's. He came back a few hours later replacing the 1/4-20 with a 8-32 screw. The unit of measurement of the Hyundai stuck.

Jump forward about 10 years, had an engineering intern. He was confused when he asked about a load on a part, and one of the engineers that worked for me told him 'a couple-a Hyundai's'.

Mike k

Want to fix a bigger problem? Find me the 1/4 inch on a 1/4-npt pipe thread.

View attachment 657683
View attachment 657687
Hyundais have gotten much, much bigger over time, so you need either a recalibration or switch to the newer KIA units.

Has anyone flown a MiG? Do Russian and Chinese aircraft use feet and knots
They use metric.

2 large bathtubs of water, 25 standard bags of cement, a cubic yard of dirt, a partly stripped "Smart" car, a pallet of bricks. 2 or 3 grand pianos...

Are we talking long tons, short tons, or metric tons?

Years ago, I had a young engineer that worked for me, Smart guy but no real life experience. He came to me with a design for a 'small aircraft part' and it has 1/4-20 bolts on it. I'm looking at this thinking that he is really missing something in his design and analysis, 1/4-20 is a pretty big bolt for small aircraft parts. I told him that a bolt like that can hold a 'a few tons' in single shear. I could tell that a number like a few tons didn't register with him. At the time he drove a 80's Hyundai Excel, When I told him a 1/4-20 bolt could hold 'a couple of Hyundai's' suspended, his eyes got wide, and I could tell that he could think in terms of Hyundai's.
This is an exaggeration or you are remembering the bolt size incorrectly. Back when the AISC manual gave simple direct values for bolt capacity, the allowable tension load on a 3/4" diameter bolt was 6690 pounds and the allowable single shear capacity was 4420 pounds. A 1/4-20 bolt has 11% of the cross section area of a 3/4" diameter bolt so the corresponding allowable loads would be 743 pounds in tension and 491 pounds in single shear.

Consider an older American car with a big V8 engine in it- the only pieces bolted on with 1/4-20 were sheet metal pieces like the valve covers. Everything else used larger bolt sizes including alternator and so forth. When I worked in my dad's shop we pulled out a lot of motors. We had a plate with 4 holes in it and a loop welded on it, we would remove the carburetor and put that plate in its place, bolt in on with 4 5/16 bolts and use that to pull the engine out, engines that weighed 500-700 pounds.

One of my pet peeves is the common belief that nominal pipe sizes are measured by the inside diameter. Yes, it's classified by the "nominal bore" terminology, but it's a pretty damn loose relationship to the actual ID even cherry picking the nearest matching schedule for each nominal size.

TP

One of my pet peeves is the common belief that nominal pipe sizes are measured by the inside diameter. Yes, it's classified by the "nominal bore" terminology, but it's a pretty damn loose relationship to the actual ID even cherry picking the nearest matching schedule for each nominal size.

TP
Man........., don't get me started on the metricated impetric pipe sizes we have in Australia. Aaaaaaaaaagh.

This is an exaggeration or you are remembering the bolt size incorrectly. Back when the AISC manual gave simple direct values for bolt capacity, the allowable tension load on a 3/4" diameter bolt was 6690 pounds and the allowable single shear capacity was 4420 pounds. A 1/4-20 bolt has 11% of the cross section area of a 3/4" diameter bolt so the corresponding allowable loads would be 743 pounds in tension and 491 pounds in single shear.

Consider an older American car with a big V8 engine in it- the only pieces bolted on with 1/4-20 were sheet metal pieces like the valve covers. Everything else used larger bolt sizes including alternator and so forth. When I worked in my dad's shop we pulled out a lot of motors. We had a plate with 4 holes in it and a loop welded on it, we would remove the carburetor and put that plate in its place, bolt in on with 4 5/16 bolts and use that to pull the engine out, engines that weighed 500-700 pounds.
Tension is not shear. Presumably, for an aircraft, we are talking about an AN bolt, and 1/4-28, not 1/4-20, not that it matters if we're talking about shear. I read someplace that shear strength for a bolt might be 40 percent of tensile. So we're talking about 40 percent of 125kpsi, or 50 kpsi. Cross sectional area is about .049, so that ought to hold 2,400 lbs or so, which I think would count as a Hyundai. If you can put it in double shear, maybe two Hyundais.

Let's say "suspended" implies tension. In that case, if I'm not mistaken, the "thread stress area" is multiplied by the tensile strength to get the breaking load. For a 1/4-20, it would be something like .033 in^2, for a 1/4-28, a bit higher. So we can expect about 4,100 lbs. Two small Hyundais.

Note that kramer714 did NOT say it would be safe like this. With a safety factor of 1, things might get a bit dicy.

Man........., don't get me started on the metricated impetric pipe sizes we have in Australia. Aaaaaaaaaagh.

Metriperial measurements sh1t me to tears. Just sayin’.

BTW, I'm not sure basing engineering on how it was done in old Detroit iron with V-8 engines is the best idea. Maybe if you have too much steel and gasoline on hand and live in a dry place with cheap labor and a decent elevation above sea level......

They use metric.
Great

I was waiting for someone to jump in with metric navigation. Anyone? I think I understand how, but don't have any km based charts.

Also, the US military uses a couple kinds of grid squares especially for ordinance targeting which I believe are metric. But I don't know much.

There are some maps that use eastings and northings to locate points on the map. A zero point is defined off to the southwest of the map. The eastings and northings are just the number of meters relative to that point. Our local street directories (remember those!) even had them marked on the maps.

Tension is not shear. Presumably, for an aircraft, we are talking about an AN bolt, and 1/4-28, not 1/4-20, not that it matters if we're talking about shear. I read someplace that shear strength for a bolt might be 40 percent of tensile. So we're talking about 40 percent of 125kpsi, or 50 kpsi. Cross sectional area is about .049, so that ought to hold 2,400 lbs or so, which I think would count as a Hyundai. If you can put it in double shear, maybe two Hyundais.

Let's say "suspended" implies tension. In that case, if I'm not mistaken, the "thread stress area" is multiplied by the tensile strength to get the breaking load. For a 1/4-20, it would be something like .033 in^2, for a 1/4-28, a bit higher. So we can expect about 4,100 lbs. Two small Hyundais.

Note that kramer714 did NOT say it would be safe like this. With a safety factor of 1, things might get a bit dicy.
Allowable stress in shear for something like a steel beam used to be 40% of yield strength but allowable stress in tension was 60% of yield strength so basically allowable shear stress was 2/3 of allowable tension stress. Bolts were always specified differently. If we're going to talk about Grade 5 bolts which are 120ksi ultimate strength then allowable tension was 40ksi and allowable shear through the body of the bolt was 22ksi.

I gave both tension and the shear values in the first reply, for common bolts the shear value is 2/3 or less of the tension value. High strength bolt would be of course higher strength but are those commonly used in sizes like 1/4-20 and #8? I searched and found they are available in 1/4 diameter but not shown for anything smaller than that. If you can get ultimate strength of 120ksi in a 1/4-20 bolt then you could carry about twice the load I gave. Common bolts have ultimate strength plus or minus 60ksi. I doubt if a small aircraft part utilizes double shear and the original discussion specifically said single shear. Below is the relevant AISC table for 120ksi bolts (A325)- single shear 9720 if you are shearing through the body of the bolt and not the threads, significantly less if you shear through the threads. Convert this to a 1/4" bolt and you get 1080 pounds. That's about half of a really old Hyundai so now it's just the factor of 2 in the wrong place.

One of my pet peeves is the common belief that nominal pipe sizes are measured by the inside diameter. Yes, it's classified by the "nominal bore" terminology, but it's a pretty damn loose relationship to the actual ID even cherry picking the nearest matching schedule for each nominal size.

TP
The explanation I heard long ago is that the original iron pipe ID was the nominal size. As materials improved, they were able to get the same pressure ratings with thinner walls. However, since threaded pipes demand a constant OD to be backwards compatible, they kept the old OD and made the ID larger. This may or may not be accurate, but it has a lovely sheen of plausibility about it.

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