Define the torsional constant for a spring.

(N/A) The torsional constant (also known as the restoring torque constant) of a spring or a suspension wire is defined as the restoring torque per unit angular twist.
If a torque $\tau$ is applied to a spring,resulting in an angular twist of $\theta$,the restoring torque is given by $\tau = k\theta$,where $k$ is the torsional constant.
Therefore,$k = \frac{\tau}{\theta}$.
The $SI$ unit of the torsional constant is $\text{N} \cdot \text{m/rad}$ (Newton-meter per radian).