A US hydrographic survey tape measure.
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The Eu/Metric system of industrial hydraulics didnt like US npt so they went straight with seal rings, now you have created the issue of more machining to a housing and quality of the seal rings so risk of more leaks, yes.
Tapered fitting just work, dead simple.
Then the metric system used horrible uk bsp and used with straight threads, what a mess.
US had 2 systems SAE and AN/JIC metric added anything in your imagination to solve already solved problems.
No gain whatsever putting liquid flow fittings in metric less you can use metric wrenches.
Measurement based on 10 is logical and easy to use, no question.
US threads were designed by engineers to solve engineering problems.
Metric system when moved to threads and fittings was just fudged in to say they are metric.
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I ran an ATB that had German gearboxes. Most everything else onboard was built in the US. Kept two sets of tools. Also had greasing system components with metric tube fittings, too. First couple of months onboard were interesting. . . after that, I was used to the two systems.
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Two systems = Bigly problems. One system = No problems.
If only ONE system, one set of tools fit for all tasks on all machinery and equipment.
(Just make sure you throw away those SAE tools so you donât get confused)
If that one system is Metric, it has the advantages of being easy to understand and use.
That is why it is widely used world wide, incl. in the US apparently.
So what is the problem making it the ONLY system in use anywhere.
PS> I donât buy the statement that hydraulic fitting with metric sizes and treads leak more than those in SAE measurements.
âTwo systems = Bigly problemsâŚâ
Absolutely - but these systems have both been around for many, many years and have been adopted differently in different areas and industries - witness the pipe thread abominations described above.
If all we ever worked on were brand new equipment, with everything built in the same country to the same standard, maybe we would be able to chuck out one set of tools - but then who would maintain the old tractor? Our 20-yo yacht/home was built in Taiwan with a Japanese engine & transmission, and uses rigging bolts & hardware manufactured to Imperial standards. Short of a complete re-construction I had better keep both sets of tools 
And donât get me started on the threads on the Italian-made water heater (which is otherwise a wonderful bit of kit!).
Edit to add: What thread is present on the high & low pressure test points in the air conditioning or refrigeration system in an otherwise all-metric automobile or vessel?
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the design is different not just a thread size change, its not like nuts and bolts in many cases.
Lots of systems have been in use in different parts of the world and in different trades for a lot of years, not only two.
That is why Henry V decided to standardize the system used in Britain by adapting measurements of his own body; i.e. Feet, Hands, Thumbs (Inch) and arms (Fathom)
Maybe it is time to let a long dead King RIP and adapt fully the same system as >95% of the world is using.
No it is not done over night, nor has it been in the countries that has adapted the metric/SI system as the only official system of measurements.
Norway went metric in 1873, but still smaller boats are defined by their length in feet by most people. Planks and board were until recently measured in inches for thickness, but length in meters.
Fishermen measured their Spats catch in âSjeppeâ (20 ltr.):
While herring were measured in âHektoliterâ (100 ltr.):
Not sure when that official change to Kg and Tonnes respectively.
Donât worry, the veteran car, tractor or boat motor enthusiasts will be able to keep their old tools, even if the professional workshops are able to get rid of theirs.
PS> Both Norway and Sweden have kept the mile (Mil). It is in common use, but adopted it to be defined as 10 Km. The official measurement for road distances are in Km., however.
Car fuel consumption is advertised in âLtr./Milâ.not âKm/Ltr.â
!00% agree. The first time I saw a BS straight thread fitting my reaction was, WTF is this little rubber gasket piece for? If it is tapered it wonât leak, is the supplier getting a kickback from the little rubber gasket guys? I can accept metric but are you not capable of tapering threads in decimal, it is not that difficult. Things have gotten marginally better since then. They learned to do some primitive tapering, to whose standards? I donât know but the bar must be low.
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There is obviously a lot of things about threads and fittings that I, not being an Engineer, didnât know. There are an awful lot of different standards to chose from by the look of it.
It does appear the that metric tapered threads does exist though:
PS> I donât know how common metric tapered threads are? Are they mostly used in Europe?
How about metric self tapping screws, another wtf
Can I have a 10guage screw 35mm long thanks, certainly sir.
I like when people jam NPT into BSPP and say âitâs close enough!â Great.
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I wish we could go metric in the galley. And measure everything by weight. Try finding a prep cook these days who knows fractions at all. Told the prep cook to multiply the cookie recipe times 4. He couldnât as we had no internet and he was used to googling things like what is 4 times a 1/4 cup. Easier to give him a scale and cheap calculator. Go to a deli counter and ask for 3/8 of a pound of something, and youâll see what I mean.
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You mean like this?:
What is the joke?
The screw thread sizes are in gauge but the length is metric, another fudged to fit metric system.
Here is where they came from
Hereâs another
1" to a foot, god knows if they tried to make that metric?
Believe it or not there was some metric inventions, well one that I can think of.
There are some items that were invented in metric and have been in common use in USA equipment and worldwide for almost 100 yearsâŚ
Hereâs the part number for one 6206, still remember that from teenager yearsâŚ
Some of the ginger beers here might know that one as well fixing cars trucks etc.
Man who cares just put a bigger self tapper in there next time!
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stick a match or tooth pick in as wellâŚ
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Oh well, you are right, Imperial Units are better for some application, others may require metrics (or a match/tooth pick) to fit.
Just donât mix in SAE, NPT, UTS, CSU or the rest of the âalphabet soupâ of standard units in use around the world.
As for screws, you only have to memorize this Conversion table and you got Imperial and Metric units covered:
https://www.accu.co.uk/en/p/72-metric-imperial-conversion-table
Alternatively we say; âthe hell with this BSâ and look for a toothpick. or two
Nonsense, cross threading is just as effective as loctite.
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Only if you double wrench it.
Yes tapered threads are used in Europe or anywhere people donât want to use gaskets to stop fittings from leaking. The problem is when you go to shipyards in Singapore, Korea, China, US, Finland or any other country you never know what standard they are using. It depends on where each piece of equipment was sourced from. Yes the diameter may be metric but WTF⌠which metric? JIS, BSP, BSPT, MT, can all be measured in metric but they donât properly match. There is NO international standard even though people claim metric is the standard, but which metric? Adopt a straight thread standard and a tapered standard and be done with it. It is not that difficult to set up machines to make any thread but a standard has to be adopted. I have had to stock all the above thread types in the same diameter on ships for repairs. Waste of money and more than a little annoying.