IN the design of aircraft structures for fatigue strength, it is as well to bear in mind that those parts most likely to give trouble fatigue‐wise are those wherein rivets or bolts have to react a load. The term ‘react’ is used here to distinguish this from the case where rivets or bolts arc used to hold the skin on the frame, etc., where the worst possible concentration of stress in terms of the nominal gross area will approach that of a hole in an infinitely wide sheet, or about 3·0. The riveted joint is more likely to approach that of a lug, which, for conventional rivet spacing and edge distance would be about 5½ in terms of gross stress. In other words, our working stress for a joint would be about one‐half the axial stress in a plain sheet with holes for the same life. Other things, such as normal loads and buckling, may alter this ratio somewhat.