SRKi Lightweight Water Pump Pulley weighs about 215 grams, or about 0.47 lb, and is manufactured in Korea using aircraft-grade aluminum.
Factory water pump pulley weighs 340 grams, or about 0.74 lb.
Pulleys are the same diameter as the factory pulleys with lower weights, resulting in less rotating mass and less power lost, and faster engine response in the case of the crank pulley.