The shear stress due to torsion is computed with the torsion formula:

$\mathrm{\tau }=\frac{\mathrm{Tc}}{\mathrm{J}}$

Rearranging this equation to solve for the torque $\mathrm{T}$ that produces the limiting $50 \mathrm{MPa}$ shear stress:

$\mathrm{T}=\frac{\mathrm{\tau J}}{\mathrm{c}}=\frac{(50 \mathrm{N}/{\mathrm{mm}}^2)(1,353,830.1 {\mathrm{mm}}^4)}{37.5 \mathrm{mm}}=1,805,106.8 \mathrm{N}-\mathrm{mm}$