A rotary hook of a lockstitch sewing machine includes at least one hook body including a cylindrical cavity and a basket freely rotatable in the cylindrical cavity, to which it is constrained by a rib, provided on the outer surface of the basket, which engages in a C-shaped race, provided in the inner wall of the cylindrical cavity of the hook body and delimited by two plane surfaces parallel to each other and by a cylindrical surface perpendicular to the plane ones, suitable to prevent axial and radial translation of the basket in the cylindrical cavity—further includes elements applying to the basket an axial pressure causing the rib of the basket to lean against one of the plane surfaces delimiting the race present in the cylindrical cavity of the hook body. Some of these elements are carried by the lockstitch sewing machine to which the rotary hook belongs.