At W.W. Grainger Inc., a Chicago-based business-to-business distributor of office and industrial supplies, mobile apps are big business. And that business is about to grow. Today, Grainger’s mobile app accounts for about 40%—$23.4 million—of the company’s 2014 Internet Retailer-estimated mobile commerce sales of $58.5 million. But within two or three years, Grainger’s mobile app, first deployed in 2012, could account for between 60% to 70% of all mobile sales. Grainger sells products ranging from paper notebooks to power tools and refrigeration equipment that companies use for their own maintenance, repair and operations—a category often referred to as MRO.