Every day, TheStreet.com Ratings compiles a list of the top 10 stocks in five categories -- fast-growth, all-around value, large-cap, mid-cap and small-cap -- and publishes these lists in the Ratings section of our Web site.The top 10 rankings are based on our ratings, which assess risk-adjusted returns as well as other criteria specific to the type of stock. We update the lists at the end of the business day on the basis of information available at the close of the previous trading session. Beginning this week, we are publishing a daily article that takes a closer look at the ratings of the stocks on one of the lists. Today we'll look at mid-cap stocks. These are stocks with a market capitalization of between $500 million and $10 billion that rate near the top of TheStreet.com Ratings' coverage universe. In addition, the stocks must be followed by at least one financial analyst who posts earnings estimates on IBES. The stocks are ranked in the order of their potential to appreciate. Gorman-Rupp ( GRC), which designs, makes and sells pumps and related equipment for use in construction, industrial, petroleum, agricultural, fire and military applications, has been rated a buy since November 2005. The company's gross profit margin for the third quarter of its fiscal year 2006 increased from the same period a year earlier. It managed to grow both sales and net income at a faster pace than the average competitor in its industry. Gorman-Rupp is also extremely liquid, and it increased its liquidity in the fiscal third quarter over the year-earlier period, indicating improved cash flow.