NGK GR8DI - 8 Spark Plug for Rotax Max Evo Engines. This spark plug is one of the two 'spec' plugs for Rotax legal kart racing.
This plug is the 'cooler' of the two plugs that Rotax allows for racing - for air density less than 75% and ambient temperatures more than 75 degrees this plug is likely almost always the best plug to run. Below those thresholds (or above in the case of air density), you may want to consider the NGK GR8-DI.
Note: Always check the Rotax regulations for your local series when selecting spark plugs, to make sure you are in technical compliance.