It is too bad we don't have a US plumber or piping engineer on this list to settle this, so I will do my best.
In the US, for good, bad, or otherwise, the following conventions hold for traditional pipe and tubing sizes. For pipe: The published size is based on the nominal ID. Thus, 1/2 inch pipe will have a nominal inside diameter of 0.5 inches and an outside diameter of approximately 0.75 inches This does not matter if it is iron, galvanized, copper, or plastic. It will be the ID that counts and the OD may vary. For Tubing: The published sizes are based on the OD. Therefore, 1/4 inch tubing will have an outside diameter of 0.25 inches, while the ID will depend on the wall thickness of the material, thus causing the ID measurements to vary. Conduit is yet another beast: It depends on the material and type, which relates to wall thickness. I believe the sizes are based on inside diameter. My employer is converting to metric units depending on the requirements of the customer. Since I don't deal with the piping and structural guys very much, I am not yet familiar with how the units are applied, or converted. I just know that all of our control system vendors document and deliver their control cabinets in mm. Aaron Harper On Fri, Apr 10, 2009 at 7:50 AM, Jeremiah MacGregor < [email protected]> wrote: > That depends on what you mean by inch based. Spanish plumbers as well as > all others in the world (except the US) buy their pipe by metre lengths. > > Pipe diameters are express using inch trade names but don't measure > according to the name. A half inch pipe is no where near a half inch. It > is much, much bigger.. > > Recently the ISO establish metric names for the pipes based on a closer > metric dimension. A half inch pipe has a metric designation of DN15. I > have done something you hate to do and actually measured some pipe. I have > some half inch (12.7 mm) electrical conduit that measures 16 mm ID, is 1 mm > thick and has an 18 mm OD. I find it strange that the pipe is actually 3 mm > plus larger then the imperial trade name. Care to explain why? > > Care also to explain why you are satisfied with the use of a name that does > not reflect the real dimension? > > Why do you confuse trade names with actual measurements? > > Jerry > > ------------------------------ > *From:* Stephen Humphreys <[email protected]> > *To:* U.S. Metric Association <[email protected]> > *Sent:* Monday, April 6, 2009 8:03:44 PM > *Subject:* [USMA:44459] RE: Reasoable Language (was Metrication US) > > There's the odd exception - eg TV's. > > Also - isn't Spanish plumbing based on inches for some historical reason? > > ------------------------------ > Date: Mon, 6 Apr 2009 12:28:59 -0700 > Subject: [USMA:44449] RE: Reasoable Language (was Metrication US) > From: [email protected] > CC: [email protected] > To: [email protected] > > > The Spanish word for inch is "pulgada." Like most words for inch, it is > similar to word for "thumb," which in this case is "pulgar." Of course no > Spanish-speaking country uses inches or feet. Naturally the original > pulgada, pre-metrication, was not equal to 25.4 mm or the barley-based > system you mention. But the word "pulgada" now refers to the 25.4 mm > international inch. Similarly the word "pie" means "foot," in both the > measurement and anatomy. > > Stephen Mangum > > On Sun, Apr 5, 2009 at 7:26 PM, Jeremiah MacGregor < > [email protected]> wrote: > > Martin, > > I agree that the duim is a body part that some people used it to measure > things with in the past like the foot. I don't agree that it is the same as > the inch. The inch was defined as three barley corns round and dry. Can > you tell me the original official definition of the duim? I would suspect > that it was not related to barley corns. Thus my point is, the two are not > the same. No disrespect was intended. > > I'm sure we can find a list of units that were used in various countries > that have no equivalent to English units. > > Jerry > > ------------------------------ > *From:* Martin Vlietstra <[email protected]> > *To:* [email protected]; U.S. Metric Association < > [email protected]> > *Sent:* Sunday, April 5, 2009 3:53:03 PM > *Subject:* RE: [USMA:44374] RE: Reasoable Language (was Metrication US) > > Jerry, > > Two things: > > 1) Please do Han the courtesy of assuming that is command of Dutch is > better than yours – the “.nl” at the end of his e-mail address suggests to > me that Dutch is probably his mother tongue.. > > 2) I can vouch for the fact that the word “duim” means both “thumb” and > “inch” in both Dutch and Afrikaans (I speak both languages). In English, > the word “foot” can either be part of the human anatomy or it can be a unit > of measure. In Dutch and in Afrikaans, both the words “voet” and “duim” are > units of measure and are also parts of the human anatomy. > ------------------------------ > *From:* [email protected] [mailto:[email protected]] *On > Behalf Of *Jeremiah MacGregor > *Sent:* 05 April 2009 14:28 > *To:* U.S. Metric Association > *Subject:* [USMA:44374] RE: Reasoable Language (was Metrication US ) > > … snip > > Doesn't the word "Duimstok" literally mean "thumb stick"? A thumb and an > inch are not really they same thing, even if they are close. > > … snip > > Jerry > > ------------------------------ > > *From:* Han Maenen < [email protected] > > *To:* U.S. Metric Association <[email protected]> > *Sent:* Sunday, April 5, 2009 5:54:11 AM > *Subject:* [USMA:44369] RE: Reasoable Language (was Metrication US ) > I agree with Bll Potts. Leave expressions like 'inch by inch' or 'not an > inch' alone. Those opposed to metric would love it if we wanted to change > such things. > In the Netherlands a folding measuring stick is called a 'duimstok', which > is 'inch stick' in English. I have a wooden duimstok or inch stick with > centimetres only on it. I just avoid measuring instruments with dual units > like the plague. > > Just west of of Dublin is the suburb Inchicore, how lunatic it would be to > change that to 2.54cmcore, or Sixmilebridge near Limerick to '9.6 > km-Bridge'. Of course, the distance to Sixmilebridge is always given in km > on road signs: 'Sixmilebridge 10 km'. There is a small place in Ireland > called Inch. > > And people in metric countries should never give an inch to Imperial and/or > U.S. Customary in their own environment. That would be very beneficial to > metrication. > > Han > > > ----- Original Message ----- > > *From:* Bill Potts <[email protected]> > *To:* U.S. Metric Association <[email protected]> > *Sent:* Monday, 2009, March 30 22:30 > *Subject:* [USMA:44234] RE: Reasonable Language (was Metrication US ) > > Pat and John: > > For years, some of us on this list have tried to be reassuring to the > metrication-averse and to also counter some of the stranger statements made > by the more virulent opponents of metrication. > > <snip> > > > > > > > > -- > Stephen > > ------------------------------ > Share your photos with Windows Live Photos – Free. Try it > Now!<http://clk.atdmt.com/UKM/go/134665338/direct/01/> > >
