Two steel plates are connected by a pair of splice plates with eight bolts as shown. The ultimate strength of the bolts is $270 \mathrm{MPa}$. An axial tension load of $\mathrm{P}=480 \mathrm{kN}$ is transmitted by the steel plates.

If a factor of safety of $1.6$ with respect to failure by fracture is specified, determine the minimum acceptable diameter $\mathrm{d}$ for the bolts.