Calculation of Pins

Figure$-1\mathrm{.}2$ shows the connection of a gear wheel to the shaft with a radial pin. Under the influence of the torque Ma transmitted

by the connection, the pin is forced to be cut, and the bearing surfaces of the pin and the shaft and hub are forced to be crushed. D

Accordingly, the tangential force that forces the pin to cut is and the shear stresses in the pin are;

$=\frac{F_t}{2\frac{d_p^2}{4}}=\frac{4M_d}{*d_p^2*d}{}_{em}$

It is written as $.$

A$-$A section Where does The $2$ come from in shear stress equation?