Abstract: This invention comprises an attachment for a spark plug which is to be used in place of the usual washer normally inserted between the seat of the plug and the engine block. It comprises a heat conducting sleeve which fits over the threaded end of the plug and extends part way up the body of the plug. The surface of the outer end of the sleeve conforms with the seat in the engine block, so that the sleeve can fit snugly between the engine block and the plug when the plug is screwed into the engine block. The surface of the attachment forming the seat is provided with radial grooves which permit air to pass to the threads during the intake stroke of the engine. This feature, together with the ability to conduct heat rapidly away from the plug, increasing the efficiency of the engine by providing more complete combustion and at the same time decreases the tendancy of the plug to foul and thus increases the life of the plug.