Many U.S. industrial companies' shares that slid last year over concerns of an economic slowdown have regained their footing in recent weeks, but some investors and analysts suspect the stocks still may be standing on uncertain ground. Shares of about 10 large industrial manufacturers and distributors, such as Caterpillar Inc., Parker-Hannifin Corp. and Eaton Corp Plc, have climbed between roughly 5 percent and 15 percent this year, although most have not recouped significant declines they suffered in 2015.