he wasn’t going to be any more specific

He pointed up again: “Can you see there, the gob going down?” A big blob, glowing white, was hanging off the end of an enormous clear glass tube. That one tube, he said, would produce a few thousand kilometers of glass strand. He smiled; he wasn’t going to be any more specific. “This is the top of the draw,” he said. “We’re going to go down a few floors.”

We ran down the stairs, with me clattering after Mazzali. He opened the door on the floor just below where we had been and pointed ahead of us: “Can you see the fiber?” he asked. “No,” I said. “Look carefully,” he said. And there it was, an impossibly thin strand, descending from a big hole in the ceiling to the floor. “Now you’re going to see the last stage, which is putting it on a spool,” he said.
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We clattered down more stairs into the basement. There a calm, tall man named Matt was watching gauges as the strand of fiber wound onto a spool. He was looking for imperfections. “Remember that the fiber is 125 microns in diameter, plus or minus less than a micron,” Mazzali said.
“We have to control the diameter of this glass, every single meter of it, over more than a thousand kilometers, by all of this equipment that we have on the draw, the tension, the temperature, the speed, and all that,” so that whenever a splice has to be made—a connection between one strand of fiber-optic cable and another—the fiber will transmit perfectly.