It's not hard, but it is expensive. So why not fake it and pocket the difference? It's not like that would literally kill people

OK then spell out your name 10 nm across and send me a pic of the electron microscope

It's not necessarily about difficulty. It's mostly about risk and consequences. If a company fucks up the screws I buy to hang up pictures, I might get a dent in my floor or a bigger hole in my wall. If a company fucks up the screws keeping a plane together, it might fall out of the sky.

Then why is it literally my job to work on machines that sole purpose is to find parts, yes aircraft fasteners even, that are not up to specification and reject them? If your metal is porous, it is weak. If your threads don't make proper contact, they sheer, if the nut head is off perpendicular, it cracks. I could go on.

These parts are rejected because their particular variances make them unaccountable; they will not behave as modeled. If you think it is not hard, I would love to know your method for producing oh something like 300 fasteners a minute with that degree of precision. If our machines let even one bad part through, we're rediscussing our contract. A 5% false reject rate is considered acceptable over having any bad part go good...

It is difficult, wouldn't you say? Its a goddamn modern miracle, screws damnit

PS also we work in micrometers, if you actually knew how small nanometers are.. well you wouldnt have said that, cheers to learning