KLG sparking plug, type Ks1, 1935.
© Science Museum / Science & Society Picture Library
Sparking plugs provide a spark of high-voltage electricity to ignite the mixture of fuel and air in the cylinders of a petrol engine. They are screwed into the cylinder head with a spark gap provided between an insulated electrode and one or more earthed points. This example is a mica-insulated, two-piece, detachable plug suitable for sports car engines where a very high heat resistance is necesary.