The ultimate shear strength of the bolts is $270 \mathrm{MPa}$, and a factor of safety of $1.6$ with respect to fracture is specified. The allowable shear stress for the bolts is therefore:

${\mathrm{\tau }}_{\mathrm{allow}}=\frac{{\mathrm{\tau }}_{\mathrm{fracture}}}{\mathrm{FS}}=\frac{270 \mathrm{MPa}}{1.6}=168.75 \mathrm{MPa}$

Note: The ultimate strength is the fracture stress of the material.