Really boring hats are selling quickly, Elon Musk said on Sunday.

Musk, the CEO of Tesla, SpaceX, and the Boring Company, was talking of course about the painfully boring, black baseball cap bearing the logo of The Boring Company, his very real endeavor to build transportation tunnels beneath the earth, through which hyperloop pods might travel and cars might zip along on top of electric skates. The hat sales go toward paying for Musk’s latest slightly crazy-but-it-just-might-work idea.

“To preserve the transcendent majesty & specialness of The Boring Company cap, we are capping cap orders at 50,000 caps. Almost there …,” Musk tweeted on Sunday.

And when a Twitter user did the quick math to determine that 50,000 hats sold equals $1 million, Musk seemed to acknowledge the fundraising goal, replying, “busted.”

A few minutes later, Musk joked that “Every 5,000th buyer of our boringly boring hat will get a free hat signed by the delivery guy.” Later, Musk tweeted this: “That special hat delivery will take place deep within the real, but fictional (of course), tunnel we are building under LA while you drive the giant machine blindfolded. This will actually happen.”

Elon Musk in January 2016, first bringing up his tunnels idea. He would announce the Boring Company officially in December 2016. A year later, the project continues and hat sales are hot.

The idea seemed like a joke when I saw Musk first introduce his tunnels notion at Texas A&M University in January 2016, nearly two years ago. Speaking to student teams who were showing off their hyperloop transportation pod designs, Musk said, “Tunnels are great. It’s just a hole in the ground,” he deadpanned, to laughs from students.

He continued: “It’s not that hard, but if you have tunnels in cities, it would massively alleviate congestion. You could have tunnels at all different levels, you could have 30 layers of tunnels and completely relieve the congestion problem in high-density cities. So, I highly suggest tunnels.”

Musk didn’t publicly mention the tunnel idea again for nearly a year, on December 17, 2016, when he first introduced the Boring Company: “Traffic is driving me nuts. Am going to build a tunnel boring machine and just start digging. It shall be called ‘The Boring Company.’ Boring, it’s what we do.” He later added, “I am actually going to do this.”

In 2017, the Boring Company took off in actual work performed, and media coverage — including this Bloomberg Businesweek cover story — followed.

Nice.

In April, Musk calmed the nerves of both Tesla investors and companies with which SpaceX has contracts when he said Boring Company operations take up maybe “2 or 3 percent” of his time.

“This is basically interns and people doing it part-time,” Musk said at the TED conference in Vancouver. “We bought some second-hand machinery; it’s kind of puttering along but it’s making good progress.”

The Boring Company is digging a test tunnel with a massive used boring machine Musk cheekily named Godot. The dig site is behind SpaceX’s headquarters in Hawthorne, California.

Entry hole, staging area and starting tunnel for Boring Machine 1 (aka Godot) now complete

A post shared by Elon Musk (@elonmusk) on

Musk announced on Twitter on Thursday night that the Boring Company would compete for a contract with the city of Chicago to build a “high-speed Loop connecting Chicago O’Hare Airport to downtown;” it’s unclear if that project will require a tunnel to span the full journey.

In July, Musk said he had received “verbal approval” for a hyperloop that would connect New York City to Washington, D.C. “Just received verbal govt approval for the Boring Company to build an underground NY-Phil-Balt-DC Hyperloop,” Musk posted on his Twitter page Thursday. He added, “NY-DC in 29 mins. City center to city center in each case, with up to a dozen or more entry/exit elevators in each city.”

Earlier this year, Musk said he wanted to build an LA route from Los Angeles International Airport to Culver City, Santa Monica, Westwood, and Sherman Oaks.

And the cash for every $20 hat sold, as Musk tweeted recently, “goes directly towards more boring.” The hats arrive three to four weeks later.