To facilitate manufacture, and provide readily accessible insertion openings for rectifier diodes in automotive alternators, the end covers or end shields are made as sheet metal elements with radially extending arms, leaving space for ventilating openings therebetween, extending from the center of rotation of the alternator, and form with bearing retaining means at the center, for example in the form of a punch or drawn bushing extension extending in axial direction and at right angles to the major plane of the sheet metal element which, preferably, is also formed with stiffening ribs or beads at the lateral edges thereof. Preferably, the alternator is, in cross section, hexagonal and three arms, extending at 120.degree. with respect to each other, the hexagonal outer end portions, are provided to permit universal fitting of the electrical connections with respect to the rotary position of the alternator shell and thus permit matching of the position of electrical connection to various attachment positions of the shell on an internal combustion engine.