Classes 10 (30% Cu), 11 (25% Cu), and 12 (20% Cu) are sintered metals of copper and tungsten. These combinations produce dense, hard metals with optimum wear resistance and strength at high temperatures. They also have good thermal and electrical conductivity. Refractory metals are used as facing material on spot welding electrodes where heat balance or mechanical wear resistance is needed. The additional cost of these refractory metals is outweighed by the lower production cost per weld due to longer tool life, less electrode dressing time, and high stability which provides uniform heating and prevents misalignments for higher weld quality.