Caterpillar has exercised a warrant and purchased 1 million shares of rubber-tracked vehicles and components maker ASV at a cost of $21 per share. The Grand Rapids company is a key supplier to Caterpillar and about half of ASV’s sales are to Caterpillar, according to Tom Karges, ASV's chief financial officer. The $21 million infusion will be used to build its dealer network, continue research and development and increase production. Caterpillar has options for another 8.7 million shares of ASV and if exercised would give it a majority stake. Currently, Caterpillar owns 21.8 percent of ASV’s shares.