Next time you zip up, or zip down, check out your zipper. There’s a good chance it’ll say YKK.

But, what is YKK? I head to South Gate, California, to find out.

At Koos Manufacturing in South Gate, they make AG jeans, with YKK zippers. Yul Ku, the owner of the company, shows me around. And it’s a sight. Cutting. Lasering. They make 10,000 pairs of AG jeans a day. There are men whose job it is to buff the butts of the jeans to make them soft.

And, at the very beginning of the process, there are people sewing zippers into the fly, adding sliders to the zipper chain. YKK zippers.

Ku says he’s used them for decades. “Once I started using YKK, I never thought about someone else,” he says. “YKK is a good zipper.” And what exactly is a “good” zipper? One that doesn’t break, says Ku. You don’t want a bad zipper ruining a $150 pair of jeans.

YKK, it turns out, is a Japanese company. (It stands for Yoshida Kogyo Kabushikikaisha–far too long to print on a zipper.) It’s got about half of the world’s zipper business. And it has a zipper factory in Macon, Georgia, where they make about 5 million zippers a day.

They melt copper. Turn it to wire. Make the zipper tape and tab and teeth. Give the zipper a lock , that works when the tab is in the up or down position. There are a dozen or so steps in the production process.

And, at the end: Voila! Your standard blue-jean zipper.

They make a whole lot of other zippers, too. “You have molded, injected products made out of acetel or nylon resins,” says Lee Smith, vice president of manufacturing operations for YKK (U.S.A.) Inc. He says they make zippers in 9,500 colors—including 20 shades of black. “We have a number of zippers where someone wearing a bomb suit or something, where you have quick release.”

Zipper R&D is a real job.

But these aren’t easy days to be in the zipper industry. “It has changed dramatically over the last 15 years,” says Alex Gregory , CEO of YKK Corporation of America, “as a lot of brand holders who were sewing products in the United States and Central America have started sourcing products from around the world.” Today fasteners make up less than half of YKK’s sales. The company also makes architectural products.

But the zipper is still what YKK is known for. The humble zipper. That keeps our pants up. Our backpacks closed.

Gervis Byron has made zippers at YKK for 38 years. I ask her how it feels to know that she had a hand in making the zippers we use every day. “I feel proud,” she says, “very proud of YKK.”