Over the last 15 years, Elon Musk's companies have had a big impact on the rocket, electric car, and battery markets. This weekend, Musk entered yet another new market: flamethrowers. Musk's Boring Company began selling branded novelty flamethrowers for $500 apiece.

"Obviously, a flamethrower is a super terrible idea," Musk tweeted on Saturday evening. "Definitely don't buy one."

By Monday afternoon, customers had reserved 10,000 of the 20,000 units the company planned to produce.

Founded in late 2016, the Boring Company's mission is to bring down the cost of underground tunneling. But while it's working on that, it has become a platform for Musk to launch goofy side projects. Last year, Musk sold 50,000 Boring Company hats for $20 apiece.

"After 50k hats, we will start selling The Boring Company flamethrower," Musk tweeted as that sale was wrapping up.

Now Musk has made good on his pledge. He posted a video of himself playing around with a flamethrower on Saturday. While the term "flamethrower" might conjure up images of a soldier throwing enormous flames over long distances, the Boring Company flamethrower is more modest. As Quartz points out, the flame it throws looks a lot like you'd get from a roofing torch.

Musk tweeted that the Boring Company avoided regulatory headaches by keeping the flame's length under 10 feet.

Musk's other company, Tesla, is struggling to produce enough Model 3 cars to satisfy hundreds of thousands of pre-orders—many of them placed in 2016. Hopefully, the Boring Company will be able to satisfy orders for flamethrowers more quickly. The company says flamethrowers will ship in the springtime.

Update: Shortly after this story was published, Musk updated the sales figure from 7,000 to 10,000.