Editor's Note: This article is part of Inc.'s weekly report on business niches in partnership with financial information company Sageworks

Want to work in a fast-growing industry? Steer clear of private manufacturing companies.

One-third of the top 15 slowest-growing subsectors in the U.S. are related to manufacturing, a sector in which private companies have, overall, seen their rate of sales growth decline over the past few years. Most of the subsectors included on the list are related to one of three sectors: manufacturing, wholesale, or retail trade. Metal and mineral wholesalers topped the list, seeing sales drop 1.4 percent over the past year.

"Individuals looking for good business ideas and companies looking for strong investment opportunities may have cause to be wary of these industries," says Sageworks analyst Libby Bierman.

"The average privately held company is currently growing sales at a rate of nearly 9 percent per year," she says. "The industries on this list are growing sales at a rate of less than 4 percent per year, and two of the subsectors are actually seeing sales contract." 

Bierman adds that revenue growth--while an important measurement of a company’s (and industry’s) health--should always be considered alongside other financial metrics for a more complete assessment.

"It’s important to consider cash flow, liquidity, and profitability, along with sales growth, when evaluating companies and industries," she says. "That would give a more complete picture of financial health and that market’s life-cycle stage. But, nonetheless, slow revenue growth is an immediate, easy red flag to identify." 

Below is a list of the 15 slowest-growing private subsectors in the U.S., ranked by sales growth over the past year.