In part three of Hello World Shenzhen, Bloomberg Businessweek’s Ashlee Vance heads out into a city where you can't use cash or credit cards, only your smartphone, where AI facial-recognition software instantly spots and tickets jaywalkers, and where at least one factory barely needs people.

This is the society that China's government and leading tech companies are racing to make a reality, with little time to question which advancements are net positives for the rest of us.

In 2012, Apple’s chief executive, Tim 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.

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.