NGK TR55 Stock # 3951 .055 stock Heat cu
NGK TR6 Stock # 4177 .039 colder cu
NGK TR5 Stock # 2238 .039 Stock heat cu
NGK TR55VX Stock # 2885 .050 Platinum stock
NGK TR55IX Stock #7164 .059 Stock heat Iridium
Bosch Plat 4 #4458


reduce gap .004 for every 50 HP added