Despite a trade war between the United States and China and past admonishments from President Trump “to start building their damn computers and things in this country,” Apple is unlikely to bring its manufacturing closer to home.

A tiny screw illustrates why.

In 2012, Apple’s chief executive, Timothy D. Cook, went on prime-time television to announce that Apple would make a Mac computer in the United States. It would be the first Apple product in years to be manufactured by American workers, and the top-of-the-line Mac Pro would come with an unusual inscription: “Assembled in USA.”

But when Apple began making the $3,000 computer in Austin, Tex., it struggled to find enough screws, according to three people who worked on the project and spoke on the condition of anonymity because of confidentiality agreements.

In China, Apple relied on factories that can produce vast quantities of custom screws on short notice. In Texas, where they say everything is bigger, it turned out the screw suppliers were not.

Tests of new versions of the computer were hamstrung because a 20-employee machine shop that Apple’s manufacturing contractor was relying on could produce at most 1,000 screws a day.

The screw shortage was one of several problems that postponed sales of the computer for months, the people who worked on the project said. By the time the computer was ready for mass production, Apple had ordered screws from China.

The challenges in Texas illustrate problems that Apple would face if it tried to move a significant amount of manufacturing out of China. Apple has found that no country — and certainly not the United States — can match China’s combination of scale, skills, infrastructure and cost.

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