Answer
The diameter is$\frac{1}{2}$ inch.
Work Step by Step
$\frac{7}{8} - \frac{3}{16} - \frac{3}{16}$
Visual inspection shows the LCM is 16. Express as like fractions and subtract. Simplify.
$\frac{7}{8} - \frac{3}{16} - \frac{3}{16}$ = $\frac{14}{16} - \frac{3}{16} - \frac{3}{16}$ = $\frac{8}{16}$ = $\frac{1}{2}$