$$\begin{gathered} 20-\mathrm{mm} \mathrm{diameter} \mathrm{steel} \mathrm{rod} \\ \mathrm{A}=314.16 {\mathrm{mm}}^2 \\ \mathrm{E}=200 \mathrm{GPa} \\ \mathrm{\alpha }=12.0\times {10}^{-6}{/}^{\circ }\mathrm{C} \end{gathered}$$

$$\begin{gathered} {\mathrm{\tau }}_{\mathrm{bolt}}=\frac{{\mathrm{F}}_{\mathrm{bolt}}}{{\mathrm{A}}_{\mathrm{V}}} \\ \therefore {\mathrm{F}}_{\mathrm{bolt}}={\mathrm{\tau }}_{\mathrm{bolt}} {\mathrm{A}}_{\mathrm{V}} \end{gathered}$$

The bolt is in direct shear. Therefore, the bolt force is related to the allowable shear stress and the area subjected to shear stress.