Wear rate were strongly affected by ball type. The high carbon chromium steel balls resulted in the fewer weight loss of balls. Also, the predicted values of wear rate were obtained using the model equation and were plotted versus experimental data which are shown in Fig. 7. According to Fig. 7 and Table 5, predicted valuesare in very good agreement with the measured values (R2 value of 0.9676, adjusted R2 value of 0.9603 and predicted R2 value of 0.93).