What is economical joint and where does it find applications? A double riveted double cover butt joint is used to connect plates 12 mm thick. Using Unwin's formula, determine the diameter of rivet, rivet value, pitch and efficiency of joint. Adopt the following stresses; Working stress in shear in power driven rivets=100 N/mm? (MPa). Working stress in bearing in power driven rivets=300 N/mm? (MPa). For plates working stress in axial tension =156 N/mm?.