A joining part with a wing comprises a through bore defining a fastening direction perpendicular to the wing. The wing comprises at least one non-through pocket configured to reduce the stress gradient in a peripheral zone of the through bore and/or at least one relief configured to reduce the stress gradient in a peripheral zone of the through bore, the non-through pocket forming a cavity in the thickness of the wing and comprising a curved side at a distance from the peripheral edge of the through bore. The joining part may be part of a lug, such as, for an aircraft fitting.