I need an education outwith metric training , i've had so far

[Alistair Hosie]

I ordered an air fitting actually four of them in total,with a 10mm push fitting and a male half inch B S P metal screw end for to fit into a half inch threaded female pipe hole. The company sent me a ten mm push fitting with a half inch BSP threaded fitting on the other end. I keep getting a fitting with a ten mm push ok but the other end threaded is coming out at nineteen mm when half inch should be 12.5. The guy on the telephone tells me I am wrong. I asked him if I have a half inch threaded female internal pipe I can fit a male which is marked at half inch and is actually much closer to three quarters of an inch 19 mm in fact. I am dumb and dumbfounded that such a discrepancy exists simply put how can nineteen mm be a half inch which is 12.5 mm nominal??? Alistair

[Steve_Cole]

I ordered an air fitting actually four of them in total,with a 10mm push fitting and a male half inch B S P metal screw end for to fit into a half inch threaded female pipe hole. The company sent me a ten mm push fitting with a half inch BSP threaded fitting on the other end. I keep getting a fitting with a ten mm push ok but the other end threaded is coming out at nineteen mm when half inch should be 12.5. The guy on the telephone tells me I am wrong. I asked him if I have a half inch threaded female internal pipe I can fit a male which is marked at half inch and is actually much closer to three quarters of an inch 19 mm in fact. I am dumb and dumbfounded that such a discrepancy exists simply put how can nineteen mm be a half inch which is 12.5 mm nominal??? Alistair

Take a look here https://en.m.wikipedia.org/wiki/British_Standard_Pipe
Pipe threads, if I remember correctly are sized according to the bore of the pipe, not the thread itself.

Sent from my Nexus 6 using Tapatalk

[Mike Burch]

Steve is right.
Pipe is sized according to the bore. So half-inch pipe has an outside diameter greater than half an inch, the exact size depending on the wall thickness.
Tube is sized by outside diameter, so half inch tube has a narrower bore than half an inch.
Half an inch is exactly 12.7mm, by definition.

[boslab]

1/2" BSP isn't 12.5 MM, have a look at a BSP size table, all will be revealed.
Think you actually needed a 3/8 but haven't checked
Mark
1/2 BSP is the size of a radiator valve as a comparison.

[Jaakko Fagerlund]

Ah, the stupidity of imperial markings, you got to witness it first hand

[Seastar]

I think it makes sense to name pipe threads by the inside diameter of the pipe.
They taper anyway.
But then I grew up with the system.
Bill

[cameron]

Ah, the stupidity of imperial markings, you got to witness it first hand

If I had trouble understanding or dealing with Imperial marking, units, or the system itself I wouldn't be putting stupid labels on anything. Add a virtual smiley if you like.

[wierdscience]

Pipe threads aren't specified by the ID any longer as the ID changes with wall thickness.Metric pipe is no different as the stated size does not correspond to the actual dimensions of the pipe.
http://www.kellypipe.com/common-pipe...on-tables.html

If you want real confusion throw in JIS

[loose nut]

Metric and Imperial pipe, fittings and flanges etc. are interchangeable. The metric guys should do the math on that.

[Sun God]

I think it makes sense to name pipe threads by the inside diameter of the pipe.

It sure do, otherwise doing internal flow calculations is a right pain in the bum.

[boslab]

It's the difference between pipe and tube, a 1/2" pipe is one with a 1/2" hole, a 1/2" tube is the diameter of the tube, not the hole, so far anyway!, I'm sure there's an exception to every rule I know.
Probably hose or some obscure medical thing.
I used to go to a place called Hartlepool, we made steel for the 42" pipe mill, forever problems with cracking and slag inclusions, making really clean steel is hard.
Mark

[cameron]

It sure do, otherwise doing internal flow calculations is a right pain in the bum.

And would have been more of a pain in the days when calculations were done with slide rule, log and trig tables, and charts and graphs when available. And they were smart enough to make the bores of standard pipe larger than the nominal sizes so that after a few years service, when the pipes were furred up with deposits, or rust nodules, the flow characteristics were about equal to the clean, accurate to size pipes used in experimental work to develop pipe design formulas and graphs.

[Alistair Hosie]

I suppose I have very stupidly ordered a half inch assuming it would fit into a female half inch fitting and with this method half inch is not half of 25.4 I e 12.7 but instead nigh on 19mm instead. I fail to see how half inch 12.7 can be 19mm three quarter nominal size as I thought. Tomorrow it will be back to recognizing, that a half inch is 12.7 ,once again sorry MY mistake . it is like arguing a Mile and a Kilometer are the same thing. Alistair

[MattiJ]

Pipe threads aren't specified by the ID any longer as the ID changes with wall thickness.Metric pipe is no different as the stated size does not correspond to the actual dimensions of the pipe.
http://www.kellypipe.com/common-pipe...on-tables.html

Luckily in here most shops also tell the real dimensions in millimeters ie 1"/DN25 pipe is also marked as 33.7X4.0mm (OD X wall thickeness)

But tube and pipe mean the same in here, unlike in English.
http://www.commercemetals.com/tube-v...plain-english/

[wierdscience]

Luckily in here most shops also tell the real dimensions in millimeters ie 1"/DN25 pipe is also marked as 33.7X4.0mm (OD X wall thickeness)

But tube and pipe mean the same in here, unlike in English.
http://www.commercemetals.com/tube-v...plain-english/

We do the same,it's easier to go by the OD dimension with pipe.