The Dow Jones Industrials (DJINDICES:^DJI) climbed above the 25,000 mark for the first time today, and in doing so, it managed the impressive feat of rising by 5,000 points in less than a year. When you look back at how the 30 stocks in the Dow have done individually since Jan. 25, 2017, when the Dow first hit the 20,000 mark, it's striking that just a handful of components have done most of the work in lifting the average.

Just four stocks -- Boeing (NYSE:BA), UnitedHealth (NYSE:UNH), 3M (NYSE:MMM), and Caterpillar (NYSE:CAT) -- have been responsible for nearly half of the gains in the Dow over the past 11 and a half months. The bull market has lifted each one in different ways, but without their contributions, Dow 25,000 wouldn't have been possible.

New York Stock Exchange building, with angled view and three flags visible.

Image source: Getty Images.

Stock gains from Dow 20,000 to Dow 25,000

Stock

Stock Price Gain Since Jan. 25, 2017

Dow Increase Attributable to Gain

Boeing

$129.13

889 points

UnitedHealth

$63.74

439 points

3M

$61.79

425 points

Caterpillar

$59.69

411 points

Data source: Yahoo! Finance. Based on intraday gain on Jan. 4, 2018 compared to Jan. 25, 2017 close.

Boeing

Boeing continued to benefit from the soaring aerospace market, posting a better-than-75% rise since late January 2017 that led the Dow by a substantial margin. Demand for key aircraft such as the 737 MAX 10 midsized passenger jet and the 787 Dreamliner was strong during the year, and production helped to lift Boeing's revenue and profits. The aerospace giant's defense business also did well during the year, gaining ground from increased military spending by the U.S. Department of Defense and rising geopolitical tensions worldwide.

Few see any signs of slowing for Boeing. Airlines remain financially healthy and interested in modernizing their fleets. Military applications remain popular and increasingly necessary, opening up new opportunities for defense contractors. With the stars lining up for its business, Boeing has the capacity to keep doing well in the future.

Caterpillar

Caterpillar's gains of 60% during the 11.5-month period were also noteworthy. For the heavy equipment maker, the explanation was relatively simple: The industrial economy broke out of its downward slump and vaulted higher. Most of the company's customers saw more favorable financial conditions that allowed them to boost their capital spending on the equipment that Caterpillar can best provide.

The future could be even brighter for Caterpillar. The federal government hopes to pass an infrastructure initiative that could spur greater activity in the construction field, and that could add even more demand for heavy equipment. After years of cost-control discipline, Caterpillar is better-positioned than ever to take maximum advantage of the cyclical upswing.

3M

3M picked up just 33% since late January 2017, but its high share price gave it a substantial advantage over some better-performing stocks over the period. The company has done a good job of focusing its innovative spirit on its fastest-growing and most profitable business segments, while still exploring new areas that have particularly attractive potential. What 3M has called business transformation has also led to cost efficiencies as well as a faster response time to changing industry conditions.

3M's greatest strength has come from its work in the electronics and energy segment, with industrial applications also helping to contribute to organic growth. With those industries continuing to show signs of sustained gains, 3M could keep helping the Dow climb higher.

UnitedHealth

UnitedHealth has become the giant of the health insurance field, and its nearly 40% rise in the past 11 and a half months shows its leadership. Key strategic moves like choosing to move out of healthcare exchange markets without waiting for expected repeal and replacement of the Affordable Care Act proved to be prescient, as Republican lawmakers have been unable to make substantive changes to the health insurance program itself in their efforts during the late summer and fall of 2017.

UnitedHealth's profit margins are extremely high, and the healthcare coverage provider has done an exceptional job of keeping loss ratios as low as currently allowed under existing law. With many seeing healthcare reform getting another chance at passage in 2018, UnitedHealth has the capacity to see further gains.

What's next for the Dow?

After reaching 25,000 for the first time, some expect a quick rise to 30,000, while others note that a correction is long overdue. Whatever happens, though, these four stocks have distinguished themselves as leaders, and so they'll be instrumental in determining the future course of the Dow.

Dan Caplinger owns shares of Boeing. The Motley Fool recommends 3M and UnitedHealth Group. The Motley Fool has a disclosure policy.