Bond Standard Circuit Work Index: Assume the rod mill Work Index of 9.5 applies from the actual rod mill feed sizeof 19,300 mµ (although some of this work might ideally be done by crushers to achieve a rod mill F80 of 16,000 m) to a rod µ mill (circuit) product size of 1,000 µm. W1 = 9.5 x [(10 / √ 1,000) – (10 / √ 19,300)] = 2.32 kWh/t