ACCEL 8160 HP Copper Spark Plug 1 Piece C-Cut Design Copper Electrode Standard Length 16mm Thread Size 8 Pack HP Copper Spark Plug One Piece Design - Won't break off in head during removal like two piece design. Copper Core - Copper is a better conductor than Iridium or Platinum plugs. Heat Dissipation - Copper dissipates Heat Much better than other materials.