The industrials sector encompasses a broad range of companies that focus on industrial and commercial services, operations, equipment and more. Because of the breadth of industries requiring specialized equipment and services, there are many lines of business within the industrials sector. Industrials companies cover everything from airlines to farming to railroads and beyond. As a sector heavily influenced by the strength of the economy (during weak periods, industrials companies often perform below benchmarks) and which is also closely linked with emerging markets, recent years have been strong for many of these stocks.

For much of 2018, the upward trend continued for industrials names. Global manufacturing continued to grow throughout much of the year, while in the U.S. the Institute for Supply Management's indices measuring manufacturing and production rates continued to grow through November. With many corporations flush with cash through much of the year, opportunities for delivering new equipment in an effort to boost productivity were available. Manufacturing inventories were also generally low throughout 2018, signaling room for growth.

On the other hand, there were also negative pressures on the industrials sector throughout 2018. Ongoing disputes between the U.S. and China over trade impacted nearly every sector in some way, and industrials stocks felt this impact as farms, companies relying on heavy manufacturing and more were all stunted. As the Fed has raised rates four times in 2018, shares of these stocks have also faced headwinds. Further, global manufacturing rates grew, but at a slower rate than in previous years. This, combined with increasing global economic concerns, could spell trouble for industrials stocks heading into 2019.

Nonetheless, although many industrials companies have joined stocks across multiple sectors in seeing steep declines in the final weeks of the year, some stocks still saw significant gains in 2018. Below, we'll take a look at the top 5 industrials sector stocks, what set them apart in 2018, and how they're looking heading into the new year. These stocks were selected from a pool of companies trading on the NYSE and Nasdaq, with market caps of at least $4 billion. All of them are within one of the three industry groups — capital goods, commercial and professional services, and transportation — of the "Industrials" sector of the Global Industry Classification Standard. All figures below are for 2018 year-to-date as of December 17.

1. United Continental Holdings, Inc. (UAL)

Market Cap: $24.4 billion

Performance as compared with the S&P 500: 25.1% (UAL) vs. -5.6% (S&P 500)

2. TransDigm Group Incorporated (TDG)

Market Cap: $18.6 billion

Performance as compared with the S&P 500: 23.5% (TDG) vs. -5.6% (S&P 500)

3. W.W. Grainger, Inc. (GWW)

Market Cap: $16.2 billion

Performance as compared with the S&P 500: 22.9% (GWW) vs. -5.6% (S&P 500)

4. Rollins, Inc. (ROL)

Market Cap: $12.5 billion

Performance as compared with the S&P 500: 16.8% (ROL) vs. -5.6% (S&P 500)

5. CSX Corporation (CSX)

Market Cap: $58.2 billion

Performance as compared with the S&P 500: 16.0% (CSX) vs. -5.6% (S&P 500)

United Continental Holdings, Inc.

United Continental Holdings, Inc. takes the top spot for 2018 performance among industrials stocks. Formed under its current name when United and Continental Airlines merged in 2010, this Chicago-based company owns and operates United Airlines.

UAL owes much of its strong performance in 2018 to United Airlines' excellent passenger revenue. The company saw a 6.4% increase in revenue passenger miles, a popular measurement of passenger traffic, for the first 11 months of the year. The airline company also sports optimistic guidance for 2018 earnings and has continued to expand its operations over the year as well. United plans on continued expansion for 2019 as well.

TransDigm Group Incorporated

Specializing in commercial and military aerospace materials, TransDigm Group Incorporated comes in second for overall performance among industrials companies this year. The Cleveland-based company faced a difficult 2017 due to accusations of price gouging and a House of Representatives call for a Department of Defense investigation.

Fortunately, in 2018 TransDigm has made headlines for very different reasons. The company went on an acquisition spree this year, buying up Esterline Technologies, Skandia, Inc., Extant Aerospace and others. The company also posted net sales of more than $1 billion in the fourth quarter, up nearly 14% year over year, as well as a 25.1% increase in net income from continuing operations as compared with Q4 of 2017.

W.W. Grainger, Inc.

Founded in 1927, W.W. Grainger, Inc. offers a wide array of tools and supplies to businesses across spaces as diverse as automotives, plumbing, retail and more.

This year, W.W. Grainger outperformed earnings estimates in multiple quarters, prompting an increase in subsequent estimates. The company saw its stock price climb by more than 10% in November alone, thanks to recovery from an October sell-off which may have been prompted by concerns about margin. On the other hand, Grainger has also been highly susceptible to the trade dispute between China and the U.S. The company's CFO has estimated that approximately 20% of Grainger's U.S. segment cost of sales is based on product from China; fears over increased tariffs caused investor trepidation at various times throughout the year. The company also faces increased competition from online retailers like, although it has nonetheless managed to outperform the large majority of its peers in the industrials sector.

Rollins, Inc.

Rollins, Inc. owns a suite of companies dedicated to providing pest control services and products. The company serves more than 2 million customers in multiple countries.

In the third quarter, Rollins, posted revenues of just under $488 million, marking an increase of more than 8% year over year. The company's net income also climbed by almost 30% for the same period; all told, Q3 represented 50 consecutive quarters of improved revenue and earnings for the Atlanta-based operation. Rollins also bolstered revenues by 9.3% over the first three quarters of 2018. With these impressive results, it's no surprise that Rollins managed to earn a spot in the top five industrials sector performers this year.

CSX Corporation

CSX Corporation is a holding company with an array of businesses in its portfolio and a focus on rail transportation.

2018 brought gains for several of CSX's performance metrics, including train velocity, cars online and efficiency. It also kept its operating ratio low: below 60% for two quarters. On the other hand, the company has struggled this year with safety. Indeed, the second quarter brought more financial damage due to accidents than CSX had seen in the previous five years, as well as the unintended release of hazardous materials in multiple cases. Aside from this significant barrier, though, CSX looks poised for a strong 2019.