What happened 3D printer maker 3D Systems (NYSE: DDD) rocked the stock market last week, preannouncing a huge revenue beat for its fiscal fourth quarter and watching its stock price double overnight in response. After letting the stock coast higher for a few days on that news, investors began taking profits earlier this week -- but now they're back for a second bite at the apple, and 3D Systems shares are skyrocketing again, up 23.5% as of 3 p.m. EST. Image source: Getty Images. So what It's not just 3D Systems shareholders who are having a good day today, either. Shares of rival 3D printer makers Stratasys (NASDAQ: SSYS) and ExOne (NASDAQ: XONE) are up as well, rising 13.2% and 12.3%, respectively. Curiously, though, there doesn't appear to be a clear catalyst for any of these stocks moving higher today. So what are we seeing here? Is this just momentum traders betting on which stock will become "the next 3D Systems" (and, apparently, guessing that it will be 3D Systems itself)? Perhaps. There's certainly been enough momentum trading going on in the stock market these past several months for that to be the answer. Now what But there also could be another reason. Speaking at the 23rd Annual Needham Virtual Growth Conference yesterday, 3D Systems CEO Jeffrey Graves told investors that the additive manufacturing industry's "growth rates are projected to be very exciting" this year, with research suggesting sales could perhaps grow as much as 24%, according to a transcript prepared by SeekingAlpha. 3D Systems has already enjoyed a rebound in the third quarter and as its recent preannouncement showed that momentum continued in the fourth quarter, which tends to back up the market research. Granted, it remains to be seen if Stratasys and ExOne will enjoy similar bumps. But because this 24% projection concerns the whole 3D printing industry, and not just 3D Systems, it would seem there really is a reason -- other than just plain momentum -- why 3D printing stocks are going up like fireworks all across the sector today. 10 stocks we like better than 3D SystemsWhen investing geniuses David and Tom Gardner have a stock tip, it can pay to listen. After all, the newsletter they have run for over a decade, Motley Fool Stock Advisor, has tripled the market.* David and Tom just revealed what they believe are the ten best stocks for investors to buy right now... and 3D Systems wasn't one of them! That's right -- they think these 10 stocks are even better buys. See the 10 stocks *Stock Advisor returns as of November 20, 2020 Rich Smith has no position in any of the stocks mentioned. The Motley Fool recommends 3D Systems. The Motley Fool has a disclosure policy.Source