This story was originally published by Knowable Magazine.

Since May 2015, in a section of its WorldPort distribution center in Louisville, Kentucky, United Parcel Service (UPS) has been operating a spare parts warehouse with no spare parts. Instead, the facility is stocked with ultrafast 3D printers that can build up almost any plastic part that’s required, layer by layer by layer—and have it ready for UPS to deliver anywhere in the United States by morning.

“It was a no-brainer,” says Alan Amling, UPS’s vice president for corporate strategy. Storing spare parts for quick delivery was already a big moneymaker for the company, he says. UPS operates more than a thousand field-stocking locations worldwide—all full of items that somebody might need someday, maybe. The industrial customers who pay for that service have to keep the parts available because of warranty contracts, says Amling. But they hate it. “Inventory storage costs are massive,” he says. “So we started to see 3D printing as a solution.”

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