A solid round aluminium rod (made of 6061-T6) has a mean yield strength Sy = 40.0 ksi with standard deviation of 4.0 ksi, the rod is to be subjected to a mean static axial load of P = 25 kip with a standard deviation of 2.5 kip. Assume the yield strength and loads have normal distributions. Determine the design safety factor (ratio of mean strength to mean stress) that results in a reliability of 99.9999%, and determine the diameter of the aluminium rod corresponding to the design safety factor.