The figure shows a riveted connection of a lever arm to a flange. The lever arm is made of St37. The force acting on the arm makes an angle of 20° with the vertical and its value is F = 250N. Rivet safety stresses are T = 85 N/mm^2, ob = 160 N/mm^2. As the other sizes are given in the figure;
a) Find the critical rivet and calculate the force on this rivet.
b) Calculate the appropriate rivet diameter according to the cut.