Advanced engineered Champion spark plugs are designed for the critical difference in performance standing up to high temperatures, pressures and lead deposits. Champion plugs are FAA-PMA approved. Champion plugs are identified by type designations as indicated in the spark plug part number code. R – mil spec resistor erosion protection, E – Shielded 5/8-24 thread, H – shielded 3/4″ thread (all weather plug) B – 18mm mounting thread, 13/16″ reach, 7/8″ hex, M- 18mm mounting thread, 1/2″ reach, 7/8″ hex. 37 (number) indicates heat rating position ( High number 50 – hot, low number 26 cold) E – two electrode massive Y – Projected core nose. All Champion spark plugs are shipped in factory sealed plastic cases, opened packages are not returnable.