The fast-growing 3-D printing sector got a boost from Citigroup, which initiated coverage of two of the biggest dedicated companies in the business.

3D Systems Corp. and Stratasys Ltd. both hit all-time highs Monday after analyst Kenneth Wong wrote that we are "on the cusp of seeing much broader adoption across more upstream production applications and the consumer end market."

3D printing has been around for decades, but only recently has the technology allowed for much broader and much more practical uses, like braces for teeth, and still not-so-practical uses, such exact replicas of masterpieces by Vincent van Gough, frame and all.

3D Systems and Stratasys both make 3-D printing machines that pump out layers of plastics, metal and other materials to create products, some with moving parts.

Now, Wong told clients Monday, larger manufacturers are looking to add the technology to the production process.

As the cost of labor rises in developing countries, U.S. manufacturers see an opportunity in 3-D printing.

A representative at Stratasys said that the company does not comment on analyst notes. 3D Systems did not respond to an emailed request for comment. Spokesperson

Wong issued "Buy" ratings on both stocks. He gave 3D Systems a $60 price target. He gave Stratasys a $125 price target.

Shares of 3D Systems rose $3.46, or 7 percent, to close at $51.90 Monday, after hitting an all-time high of $54.08. Shares of Stratasys rose $4.22, or 4 percent, to $110.04, after hitting an all-time high of $113.49.

Another 3-D printing company, The ExOne Co. rose almost 4 percent to $70.43.