In the following video, 3D printing specialist Steve Heller and industrials analyst Blake Bos discuss two 3D printing stocks that investors should consider putting on their watchlist: IPG Photonics (NASDAQ:IPGP) and London Exchange-traded Renishaw (LSE:RSW).

Manufacturer IPG Photonics supplies high-performance fiber lasers that are used in metal and plastic 3D printer-based selective laser sintering technology. In the second quarter, IPG's 3D printing-related revenue grew by more than 100% year over year, but only represented about 2.5% of the company's total revenue for the quarter. IPG believes that if the market demand grew enough for it to sell 1,000 of its lasers -- from the less than 200 it sourced last quarter -- it would represent $70 million to $80 million in revenue, or about 10% of the company's trailing-12-month revenue.

Because of its relatively small size compared to its total revenue, it appears that IPG's 3D printing growth opportunity is more of an incremental opportunity than a major growth driver. In other words, investors considering buying IPG shares should also consider how the rest of the business is performing. In the third quarter, IPG grew its total revenue by 16% annually, increasing gross margins by 0.7%, which translated to a 30% increase in earnings per share. For the fourth quarter, analysts expect IPG to increase revenues by 16% annually to $192.4 million and to report $0.90 earnings per share.

Renishaw, a U.K-based precision measurement company, only recently entered the 3D printing space, and has already experienced "strong demand" and "growing interest" for its two laser-melting metal 3D printers, the AM125 and AM250. While the revenue Renishaw generated from the sales of its two 3D printers currently represents a very small percentage of the company's total revenue, 3D printing investors should keep an eye on the company's future 3D printing developments.

At Rapid 2014, North America's largest 3D printing conference, a rumor surfaced that Renishaw's next generation of 3D printers will offer the ability to perform in-process quality controls during a print job. As General Electric has previously highlighted, in-process quality controls could have game-changing implications for the 3D printing industry at large, because it would save considerable time, energy, and money, qualifying a 3D-printed part for a mission-critical application.

Ultimately, if you're an investor in 3D SystemsStratasysExOne, or another 3D printing company, it's important to monitor new developments from peripheral companies that could either have a material impact on your holdings or provide additional insight into your existing investments.

A full transcript follows the video below.

Blake Bos: Then we had two wild cards. We don't have a particular take on these companies yet, folks, because they were just brought up to us. We're definitely going to do some research. IPG Photonics laser company, and then Renishaw. They [Renishaw] have one 3D printer. We were very interested in those two companies.

Steve Heller: Yes. IPGP is the ticker symbol [for IPG Photonics]. What makes them interesting... it's kind of a picks-and-axes play. If there's a gold rush, you want to sell the picks and axes. That's who makes all the money, right, not the people mining for gold.

IPGP apparently supplies the majority of the lasers involved in direct metal printing. The issue is, though, there's about 300 printers being shipped each year in metal 3D printing.

Bos: Not a lot of lasers, folks.

Heller: Yes, not a lot of lasers. I haven't done the numbers yet, but it's probably a small percentage of their business. You have to look at the large dynamic of what's actually driving their business results.

Bos: Yes. If you look at IPG Photonics, and we haven't done it yet, be sure to look at what's driving those laser sales. Is 300 a big number for them, or is that just a drop in the bucket? If it's a drop in the bucket, even if 3D printer sales go crazy and go to 1,000, it might not be a big deal for IPG.

Heller: Right.

Bos: Next, Renishaw. This is a company that sounded really interesting. It's in London. They have a nice printer. We're going to be taking a look at them. Anything you had to add about Renishaw?

Heller: You know what's really interesting with them? Renishaw is a measurement company, quality assurance. They're really all about making sure products that are manufactured come out as specified -- to your specifications.

Bos: If they were in the kitchen, baking with you, they would be making sure that you measured every ingredient exactly right.

Heller: Exactly. They do that in the factory, though, not in your kitchen!

Bos: Exactly.

Heller: With that background and that pedigree, they bought a 3D printing company a few years ago, and now they have their first direct metal laser sintering printer on the market, basically at parity with the competition. It's a great printer, nothing wrong with it.

Bos: Nothing special, but nothing bad.

Heller: Yes. Nothing special, nothing bad. It's a metal 3D printer. Great.

Their next generation, though, is rumored to have analysis, layer by layer, so every layer that's printed, they're going to have data on it they can analyze. So, if a manufacturer like General Electric all of a sudden wants to know how Layer 3,682, what happened on that layer, and data, they can pull that data.

That would be an industry first, and that level of quality assurance is definitely something that needs to continue as the industry grows toward hopefully representing more of direct manufacturing.

Bos: Yes, we're going to be checking that company out in the future, folks. It's on the London Exchange. Ticker is RSW, I believe. 

Anyway, we're checking out Renishaw. That's all the companies we had takeaways for here, folks. It's been a great show. We'll bring you some more takeaways for Day 3, but thanks for watching and Fool on! 

Blake Bos has no position in any stocks mentioned. Steve Heller owns shares of 3D Systems and ExOne. The Motley Fool recommends 3D Systems, ExOne, IPG Photonics, Renishaw, and Stratasys. The Motley Fool owns shares of 3D Systems, ExOne, General Electric Company, IPG Photonics, and Stratasys. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.