Hello, I need your help in how to use this equation to calculate the Nominal diameter of Aluminum Alloy Rod

D= Square root of (4F/pi*UTS)

UTS Ultimate Tensile Strength = 73.4 ksi

YTS Yeild Tensile Strength = 68.7 Ksi

F=TBD FLB

Is it missing a number? do I need to use the Ultimate or the yield tensile strength? simply I couldnt get any right dimension...

Thanks