A rigid flange coupling is used to transmit torque of 300Nm between two coaxial shafts each of diameter 30mm (d), The materials usad for shaft. fange and bolts are alioy steel. cast iron and steol respectively. Four bolts are used to couple the flanges. The shats are keyed to the flange hub. The permissible shear stress is 120MPa for the mochine olements involved l.e. bols, shaft and keys. Use standard design value of pitch circle diameter as 3 d, tlange thickness as 0.5d. Estimate the bolt diameter in mm and permissible crushing atress in MPa [8sin]