The ratings of three Machinery stocks are down this week, according to the Portfolio Grader database. Each of these rates a “D” (“sell”) or “F” overall (“strong sell”).

Graham (AMEX:GHM) is on the decline this week, earning a D (“sell”) after receiving a C (“hold”) last week. Graham designs and builds vacuum and heat transfer equipment for process industries around the world. In Portfolio Grader’s specific subcategories of Earnings Growth, Earnings Momentum, and Sales Growth, GHM also gets an F. For a full analysis of GHM stock, visit Portfolio Grader.

The rating of TriMas Corp. (NASDAQ:TRS) declines this week from a C to a D. TriMas manufactures trailer products, recreational accessories, packaging systems, energy products and industrial specialty products for the commercial, manufacturing, and consumer markets. To get an in-depth look at TRS, get Portfolio Grader’s complete analysis of TRS stock.

Slipping from a C to a D rating, Douglas Dynamics (NYSE:PLOW) takes a hit this week. Douglas Dynamics designs, makes, and sells snow and ice control equipment for light trucks. The stock gets F’s in Earnings Momentum and Sales Growth. The stock price has dropped 4.4% over the past month, worse than 2.7% increase the S&P 500 has seen over the same period of time. For more information, get Portfolio Grader’s complete analysis of PLOW stock.

Louis Navellier’s proprietary Portfolio Grader stock ranking system assesses roughly 5,000 companies every week based on a number of fundamental and quantitative measures. Stocks are given a letter grade based on their results — with A being “strong buy,” and F being “strong sell.” Explore the tool here.