We wish to fit steel rods ( = 21.2 mm, = 0.20 mm) into the following

Question:

We wish to fit steel rods (µ = 21.2 mm, σ = 0.20 mm) into the following jig in order to make sure we can meet specifications. The process requires that 97.5% of all rods are to be within specifications. (Presume that no rod is so short that it cannot pass specifications.) What is the appropriate size L mm of the jaws of the jig? 95% of (two-sided) normally distributed data are found within ± 2σ from the mean and therefore 2.5% of the rods are too large.

21.2 + mm FAILED 2.5% L mm L mm