A double molded over method of manufacturing a lightning arrester in which a central core 1 is made of zinc oxide in a first step, then two metal end fittings 5, 6 are molded onto the end faces and over the side thereof, and finally a coating of elastomer material 7 is molded around the side wall of the central core and over side portions of the end fittings. The core may be formed of a plurality of smaller section bars of zinc oxide regularly disposed about a longitudinal axis with the end fittings molded onto the end faces and about the sides of the end bars whose end faces are partially metallized. In a further variant, a stack of zinc oxide based pellets having the same cross-sectional area as the core in the first example, with the stack having the same overall length as the core if stiffened by thermal compression with fusible metal inserted between pairs of pellets. The stack assembly is then compressed mechanically in conjunction with heat treatment to effect very good mechanical bonding. The core assembly formed thereby is treated as above.