Design a cast iron protective flange coupling to connect two shafts in order to transmit 7.5 kW at 720 r.p.m. The following permissible stresses may be used : Permissible shear stress for shaft, bolt, and key material = 33 MPa Permissible crushing stress for the bolt and key material = 60 MPa Permissible shear stress for the cast iron = 15 MPa.