#### Answer

$\frac{5}{16}$ in

#### Work Step by Step

Lets consider the formiula for tap drill size , TDS = OD – P, where OD is the outside diameter and P is the pitch
Given outside diameter is $\frac{3}{8}$ in and pitch = $\frac{1}{16}$ in
So TDS = $\frac{3}{8}$ - $\frac{1}{16}$
=$\frac{3}{8}\times$ $\frac{2}{2}$ - $\frac{1}{16}$
=$\frac{6}{16}$ - $\frac{1}{16}$
= $\frac{5}{16}$ in