"I guess the general US public can't really grasp small fractional sizes or thousands?"

The fractional sizes would get weirded and weirder as they get smaller.

1mm is ~1/32 (5/128ths is a really close approximation, but let's assume nobody is that crazy).

Right now it's ~1/4 of an inch Let's say they reduce the size 1mm.

Now which sounds better: 5.1mm, or 7/32 of an inch (or 13/64ths, which is more accurate)

434g would seem like a reasonable way to express the mass of the thing too.

Ah, but then you're mucking with the advertising. 0.96 pounds seems so much lighter than 434 grams, right?

A similar thing happened to A&W [0] with their "1/3 pound" burger selling fewer than a competitor's "1/4 pound" burger — effectively because "3" is less than "4" and fractions aren't for everyone.

[0]http://www.motherjones.com/kevin-drum/2014/07/great-third-po...

what I find crazy is machinists converting between fractions and decimal to work. i can't imagine how many mistakes must have been made because of that.

Machinists don't use fractions (in my experience). They just use thousands of an inch.

We're selective in our use of the metric system here in USA, and therefore Americans will generally have an intuitive sense for how big metric units are for some measurements but not others. If you say 5mm or 1L, no problem. If you say 250km or 22kg, not so much. Americans have an intuitive sense for long distance in miles, small volume measurements in teaspoons or cups, distances in inches, feet, and miles. But micro distances in mm are generally okay, largely due to things like nuts and bolts being largely metric, and the proliferation of beverage containers in 1L and 2L bottles and engine displacements measured in liters give us a hand there.

Maybe it was intended for the Canadian audience, where metric for length, and imperial for weight, is common?

American here: we all were taught the metric system at least as far back as the early 1970s in elementary school, and I'd say even we don't know why the heck we still see the old English system in use.

We might've been taught the metric system, but I think most Americans don't have the intuitive feel for the units in the way that we do for the English ones.

Though, it is a bit more complicated, at least for me. For example, if I'm weighing small objects/quantities, I definitely prefer grams and have a fairly good sense of how much of something there is if given a weight in grams. But larger weights, like people, etc., I use pounds. I know that a kilogram is 2.2 pounds, but if you give me a weight in kilos, I still have to convert it to pounds for it to be meaningful to me in a real world sense.

YMMV, though.

The same is true for something short in length. I understand intuitively what a millimeter is but start talking in meters for example measuring someones height and I have to do a conversion.

mm makes it sound small

we don't understand grams or kg as a daily measure so we have no idea what .435kg feels like.

A large glass of water, exactly 435 cubic centimeters of it.