Electric detonators consist of an electric fuse head, as described in Item (C) (1) above, in a tube of metal (or possibly plastics), a small charge of primary explosive (50 to 500 mg of a composition based usually on lead azide) and a somewhat larger charge of another explosive (e.g., pentrite, hexogen or tetryl). This group also includes certain electric detonators known as electric primers. These are often miniaturised, and the fuse head may be replaced by the incorporation, in the primary composition, of additives to make the composition conductive and enable it to be Fired by induction