Thomas Jaenisch und Felix Rohland, both 28, said their how-to guide, "Hatmakers: Crochet hats in your own style," came out in January 2012 and has since become Germany's best selling craft book of all time, The Local.de reported Monday.
The men said they started their hat-selling website, MyBoshi.com, in 2009 and the business has seen so much growth that they made $847,000 last year.
Jaenisch and Rohland said they began crocheting while working as ski instructors in Japan.
"There's a misconception about men not crocheting," Jaenisch told Der Spiegel. "But we wanted to try it out. We were really bored!"
The men said they were surprised by their success.
"I'm not quite sure why we're so successful. But I think the Do-It-Yourself trend hasn't yet reached its highpoint," Jaenisch said.