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Metricating US shapes

Metricating US shapes

Metricating US shapes

(OP)
I was checking drawings and it had US wide flanges listed with a metric equivalent. I thought, "You don't metricate nominal sizes." Just for grins I looked in ASTM A6/A6M. Guess what? Table A2.1 shows the designation when using metric. So for example a W12x50 is a W310x74 in metric. This really doesn't make a lot of sense to me. So what is the practical use of this? Maybe order standard US shapes from a foreign mill, you specify A6M and call it out with its metric designation. Just seems confusing as hell to me. No, no, not to me personally. I can convert. I've just seen so much confusion over the years going back and forth between Imperial and metric. It seems like if you want a US shape, you should call out a US designation and leave it at that. My guess is you really don't use the metric designation to order a US shape, even if you're ordering from outside the US. Does anyone know what the thinking is here?

RE: Metricating US shapes

In 1866, Congress authorized the use of the metric system...it will catch on anytime soon...smile

Sorry, could not resist.

I was reviewing ASTM A416/416M on prestressing steel recently and the same thing got my attention re ordering in metric with grade and diameter. Little easier with only two ordering parameters, but confusing nonetheless.

Damn, even Myanmar recently (2013) switched to the metric system. Only USA and Liberia left.

RE: Metricating US shapes

I’ll believe that the metric system is necessarily superior when its proponents adopt it for calendars and clocks. Not that that hasn’t been tried: link.

Until then…

RE: Metricating US shapes

We use mostly the same W-section, channel and angle shapes in Canada and use the metric callouts as the default. In our handbook and national specifications, that's how everything is listed except one table that includes the equivalent imperial callout. We have different steel material specifications, but from a practical standpoint most steel is certified to multiple standards, so they're generally the exact same heats that are sold in the US.

An inchxlb/ft callout doesn't give me any particularly useful information when my drawings are in mm and my math is in kN. If anything, I get annoyed that the metric callout isn't mmxN/m rather than mmxkg/m, but for engineering purposes the conversion is basically just 10, so it doesn't really matter.

RE: Metricating US shapes

@Dozer - not everyone who uses ASTM as a "standard" practices in the USA. I've had a number of SE Asian projects that use ASTM/AASHTO (which, for most materials is almost a mirror of ASTM) as the standard. Here, the metric (or SI) version would be the appropriate ones to use.

RE: Metricating US shapes

YUP....in 1975 Congress enacted the "Metric Conversion Act"....designating the metric system as the preferred method of measurement in the US.....after 40 years, only portions of the Federal government use it and very little of the private sector.

RE: Metricating US shapes

@Ron - what I liked in the early versions of ASTM on their roll-over to metric (really SI, not metric) was when reporting the compressive strength of concrete, one was to report the value to the nearest 79 kPa! (100 psi). I asked them how this was to be determined; never got an answer but they did change to the Canadian version of 0.1 MPa (100 kPa).

RE: Metricating US shapes

BigH....about 15 years ago I taught a metric system course to contractors.....most confused, blank looks I've ever gotten in any of my teaching experience! Conversion was the most difficult part. Tolerance conversions, as you noted, were a mess!!

RE: Metricating US shapes

But the rest of the worlds contractors coped with the conversion and adoption.

I recall growing up in Australia, as a very young boy and going shopping with my family to purchase fruit and veg, and meat from the butcher (do butchers even exist today?) there was a period of time (a few years I guess) whereby both lb and kg were displayed, but after the cut off date, all vendors were required to display only metric units.

RE: Metricating US shapes

Oh yes, there are still the neighbourhood butchers, fruit and veg shops, and bakeries in Australia. The big supermarket chains have tried to drive them out, but haven't succeeded...yet. I think Australia adapted to the SI system in roughly the same era as it adapted to decimal currency, so everything was changing.

RE: Metricating US shapes

Ingenuity....true. It didn't take them long to figure out that if the tape you were using matched the numbers on the drawing, it could be built.

RE: Metricating US shapes

Let's not forget that BIPM, the standard bearer of SI and keeper of the meter and kilogram standards, is located in France. Despite their being our allies in the Revolutionary War, they've not been much in high esteem since then. However, it's possible that just being European based is enough.

The US was founded by people that left and rejected the trappings of Europe, it's religions, etc. That could have something to do with it.

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RE: Metricating US shapes

Yeah - but what the grocers did was price all to 100 g - or per quarter pound - wouldn't price it to a half kg . . .

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