I am occasionally asked to specify overseas products. Many times, the challenge is not only the metric system but also the lack of American testing standards. To be honest, I don’t even know if those products are legal.
Another challenge is the general lack of product information. Local distribution is another challenge. I usually just put together a minimal specification and cross my fingers.
What do you do?
It depends on where the project may be located. We work in the Middle East primarily. Middle East follows IBC codes which makes specifying in that locale easier because we can reference US standards. Metric measurements will still be required. I wish that were true for US, too.
Depending on the project funding there may be a requirement to specify GCC sourced products. These may not be tested to US standards. Then the best source for help may be product representatives from global companies or the local design firm that is often engaged for these projects.
Metric measurements don’t concern me, although I do get a bit frustrated with unit conversions.
I compare the product information to the code requirements. Then I document the differences and deficiencies to the project architect, making certain they understand they are responsible for the code-compliance of the product selection.
For example, on a recent US project a PA selected a foreign plastic siding product. The product had European fire testing, but there was no equivalent for what is required by IBC. I documented this to the PA and suggested they have the local AHJ review and accept the product or go back to the mfr. to get documented equivalent testing. Very quickly the PA changed the product to a common US-made product.
As one of our in-house specification team, we establish basic selection criteria to start with. With few exceptions, we select products with US based testing and in-country distribution. As noted by the others, there are code requirements, best practices, and local labor/constructability considerations. If a team wants a foreign produced product, they are obligated to contact the representative and start the process. In many cases, the company has the data. What we don’t do is convert.
As a Canadian spec writer, I often end up specifying “foreign” products - many of those made in the US. Sometimes US-based testing is acceptable, but sometimes you need to run it by the AHJ.
When it comes to metric vs imperial, that too can be tricky. Because so much product comes into Canada from the US, we end up specifying 610 x 1220 mm ceiling tile - rather than 600 x 1200 mm. When the federal government insisted on true metric decades ago, we ended up paying more for those commodity products that were manufactured in much smaller production runs. God forbid you spec’d true metric ceiling grid and tried to install 2 x 4 lights and diffusers!
Maybe it’s time the US joined the rest of the world and embrace the metric system! Way easier than fractions my friends!
The old centimeter/kilogram system made a lot more sense to me than the current SI system, which was designed for scientists. You didn’t have to worry about exponents as much.
Basing lengths on millimeters instead of centimeters produces a false precision in the real world of construction. Pressures of kilograms per square centimeter were easier to visualize than pascals (grams per square meter or roughly feathers per square yard).
As a Canadian, I’m just going to say it’s really funny to see people complain / argue about the metric system. 
Wishing the US would join the rest of the geographic world (and the world of science) for units of measure. Metric is so much easier.
Juste:
when I was in the sixth grade (60 years ago) we spent the entire year doing everything in Metric because my teacher was convinced that “this will be adopted in the United States before you all graduate from High School.” Then, at the beginning of my career, the US was going to absolutely convert to metric “soon”. We even had road signs with dual distances in Washington state, and our specifications were done using dual measurements. Endless debates about “hard” vs. “soft” conversions. I think the only openly used metric measurement now is the one-liter bottle of soda.
David: many of the interior finishes our designers use are manufactured overseas and I just specify them as they are listed. (flooring, ceiling panels, tiles are usually metric products)> Those products do not normally have fire ratings, so it doesn’t matter. When it comes to non-slip testing (for flooring) we generally can find products with those.
But for the exterior, we absolutely draw the line at the NFPA 285 testing – no assembly test, it doesn’t get used. No exceptions. Not even if the owner thinks it “should be okay”. They aren’t the responsible party to that decision.
And yes, we sole-source those interior things and let the designers determine if a proposed substitution is sufficient or not.
While our interiors folks are also enamored with overseas products, I’m very cautious about flame spreads, chemical content, and durability testing that can be compared to our US codes and test methods.
Could care less about metric.
I’m old enough to remember that we were going to be metric by 1980! My physics class problems were in metric and SAE.
I worked on a government project that was designed in metric. The architects whined like a bunch of toddlers. But they whined even louder when they had to switch back to feet/inches!
I am mostly concerned about fire and other safety testing. Sometimes the products have those tests, but they are from a European testing agency. Is it illegal to install items that do not have American testing standards?
David, since the code either CBC or IBC regulates life safety criteria such as flame spread, critical radiant flux, and acoustics, I suggest using a non-code compliant product would be a liability and asking for red tag.