This document has been declared ""Stabilized"" and will no longer be subjected to periodic reviews for currency. Users are responsible for verifying references and continued suitability or technical requirements. New technology may exist. This SAE Recommended Practice describes the equipment and procedures used in obtaining preignition ratings of spark plugs. The spark plug preignition ratings obtained with the equipment and procedure specified herein are useful for comparative purposes and are not to be considered as absolute values since different numerical values may be obtained in different laboratories.