The definition of manufacturing in the U.S. is always changing.
And, each year, IndustryWeek tracks that change through the IW U.S. 500 -- an annual list of the largest publicly-held U.S. manufacturers based on revenue.
The 2014 iteration of the list features 28 newcomers, nine of which are in the petroleum industry -- by far the most heavily represented industry on the list.
The new companies come from 13 states and generated $102.9 billion in revenue -- 1.7% of the total revenue of the top 500 companies.
The reasons these companies made the list in 2014 vary. In many cases, large private companies had IPOs, making them eligible for the list for the first time. In others, companies completed acquisitions or simply experienced such unparalleled growth that they soared past the minimum revenue requirement for this year's list.
Whatever the case, the dynamics of the list -- of U.S. manufacturing -- are in constant flux.
This year, for example, Tesla (IW 500/384) cracked the top 500 for the first time as Elon Musk's luxury electric car company's sales skyrocketed.
This slideshow features a handful of the companies that joined the ranks of the IW U.S. 500 companies in 2014.