The Bond Abrasion Work Index (Ai) is used to determine the steel wear rates within grinding circuits. The Ai is determined by placing sample of a fixed particle size (+½” – ¾”) in a rotating drum with an impact paddle. The paddle is made from a 500 Brinell hardness standard alloy steel. The abrasion index is determined by the weight loss of the paddle. This test requires a minimum of 1.6 kg of sample at the required particle size.