Exchange-traded funds offer a convenient way to invest in sectors or niches that interest you. If you'd like to add some industrial companies to your portfolio but don't have the time or expertise to hand-pick a few, the Vanguard Industrials ETF (NYSEMKT:VIS) could save you a lot of trouble. Instead of trying to figure out which stocks will perform best, you can use this ETF to invest in lots of industrial companies simultaneously.

It's easy to overlook the industrial sector when Internet stocks and biotech companies can seem so much more exciting -- and full of great potential stock-appreciation. But industrial companies have a lot to offer, too. Consider, for example, that General Electric is choosing to focus more on its industrial businesses, planning to spin off its North American retail finance operations and looking to make a massive energy acquisition in Alstom's power generation business. Even Warren Buffett has high expectations from the industry, investing tens of billions in the BNSF railroad and billions more in acquisitions that focus on toolmaking, specialty chemicals, and more.

The ETF's Basics
If you want to add exposure to industrial companies to your portfolio, it makes sense to consider an ETF. There are several dozen ETFs focused on industrial companies, though (per the ETF Database), so choose wisely. This one is appealing for several reasons. For starters, it sports a much lower expense ratio -- i.e., annual fee -- than most other industrial ETFs, charging just 0.14%. It also has been a strong performer among its peers, ranking near the top over the past five years. Its recent dividend yield of about 1.05% has it in the middle of the pack.

On your own you might not have selected The Boeing Company (NYSE:BA) or Cummins (NYSE:CMI) as industrial companies for your portfolio, but the Vanguard Industrials ETF includes them among its 345 holdings, and they helped it post market-beating results over the past three and five years.

A closer look at The Boeing Company
Boeing has been serving investors well, averaging 14% annual growth over the past decade (and 13% over the past 30 years!). With its enormous $440 billion order backlog, its future seems rather bright, too. The company recently posted first-quarter results, featuring a 19% increase in its commercial revenue but a 6% drop in defense, space, and security. (More than three-quarters of its backlog is commercial orders.)

Boeing's 2013 was strong, and its new 777X, which features lower fuel and operating costs by 10% or more, has boosted expectations -- though lately the company's smaller 737s have been the ones selling most briskly. (It's also making the cockpits of the 777X and the 737 Max more similar in order to streamline training for pilots and permit them to more easily fly both planes.) Some would like to see Boeing executing better, and not encountering the kinds of production delays that plagued its 787 Dreamliner. Meanwhile, the company is aiming to cut costs in order to make the Dreamliner more profitable.

Boeing's stock yields 2.2%, and the company has been buying back several billion dollars' worth of stock, too.

A closer look at Cummins
You may not have heard of Cummins, but it's a significant industrial power, with a market cap north of $27 billion. It designs, manufactures, sells, and services diesel and natural-gas engines, among related activities.

The company recently posted its first-quarter results, with both revenue and earnings topping expectations on strong North American demand. Revenue rose 12% over year-ago levels, while net income jumped 20%. Cummins' natural-gas engines, produced in partnership with Westport Innovations (NASDAQ:WPRT), are selling well, with Westport having recently posted solid quarterly results of its own, as revenue grew 39% year-over-year. Still, bears worry about whether Cummins will lose market share to some tough competition.

Bulls, though, see much long-term potential, and expect strong growth from regions such as China. In a conference call, management recently noted that, "First quarter revenues in China including joint ventures were $720 million, an increase of 21% year-over-year." Management upped projections for China, but lowered them in the near term for India and Brazil.

Cummins stock yields 1.7%. If that doesn't seem like a lot, consider that it has increased its payout by an annual average of 29% over the past five years -- and its payout ratio is well under 50%, suggesting plenty of room for further growth.

The Big Picture
With the world's economies finally recovering and manufacturing picking up steam, industrial companies are poised to benefit. You might add some to your portfolio via an ETF, or you could simply cherry-pick some promising companies from within one, after doing your research. A well-chosen ETF can grant you instant diversification across any industry or group of companies -- and make investing in and profiting from it that much easier.