Length of Key ($L = \frac{3 \cdot F}{\tau_{allow} \cdot W}$):

Where:

• $L$ is the length of the key, in inches.
• $F$ is the force, in pounds (lb).
• $\tau_{allow}$ is the allowable shear stress, 25,000 psi.
• $W$ is the width of the key, in inches.