The Dial 6149 Variable Pulley is a highly-reliable, durable product from Dial. This 3-3/4" by 1/2" zinc pulley is designed for use with evaporative coolers. This is an adjustable motor pulley. It measures 3-3/4" diameter with a 1/2" bore. This pulley can be used on 1/2 or 3/4 Horsepower swamp cooler motors. To adjust, loosen set screw on one side of pulley and rotate half of the pulley clockwise until desired tension is reached. Re-tighten set screw.