The United Auto Workers union set a Thursday strike deadline at a key General Motors Corp. plant in Flint, Mich., that makes stamped parts, such as hoods and fenders, for GM truck assembly plants. The union said contract talks were not progressing as it had hoped. The auto maker and the union said they hope for a settlement, and talks are continuing. The plant, Flint Metal Center, is a major supplier for the three assembly plants that starting this summer will build the revamped GMC Sierra and Chevrolet Silverado pickups, GM's most important vehicle introductions this year. It employs 3,377 people. GM said it has removed dies that form parts to ensure a steady supply, and union officials said the move could force a showdown. The main issues under negotiation are worker health and safety and subcontracting work to nonunion workers, the union said. Two other GM plants in Flint have threatened to strike in recent weeks.