The question asks for the formula for the maximum torsional shear stress (\(\tau_s\)) in a helical spring when a force \(F\) acts on it, given the wire diameter \(d\) and mean coil diameter \(D\). The standard formula for maximum torsional shear stress in a helical spring is: \[ \tau_s = \frac{8FD}{\pi d^3} \] Looking at the answer choices in the image: - The first option matches this formula: \[ \frac{8FD}{\pi d^3} \] **So the correct answer is the first option:** \[ \boxed{\frac{8FD}{\pi d^3}} \]