A tangential indexable cutting insert can be used for metal cutting processes in general and for radial and axial turning of a stepped square shoulder in particular. The cutting insert exhibits 180null rotational symmetry about three mutually perpendicular axes. The cutting insert has generally nullSnull-shaped cutting edges extending between raised and lowered corners. The cutting edges and side surfaces are concave in an end view of the cutting insert. The cutting insert enables radial and axial turning operations of a square shoulder with unlimited depth of cut.