Although the rigid bar moves down $1.8 \mathrm{mm}$, rods $\left(2\right)$ will not be stretched by this amount. The first $0.5 \mathrm{mm}$ of rigid bar deflection will cause no elongation in rods $\left(2\right)$ because of the clearance in the connections at $\mathrm{A}$ and $\mathrm{C}$. Therefore, the elongation in rods $\left(2\right)$ is:

$$\begin{gathered} {\mathrm{\delta }}_2={\mathrm{v}}_{\mathrm{B}}-0.5 \mathrm{mm} \\ =1.8 \mathrm{mm}-0.5 \mathrm{mm} \\ =1.3 \mathrm{mm} \end{gathered}$$