DiamondFire E3.20 Small Engine Spark Plug with 5/8-Inch Hex Socket Replacement Spark Plug 14 mm thread diameter; .75" reach; 5/8" hex socket Designed to increase horsepower and lower emissions and increase fuel efficiency up to 13% Quicker starts; saves on fuel Replaces Champion RC12YC, RC14YC; Replaces NGK BCP4ES-11, BKR4E, BKR4E-11, BKR4EIX, BKR5E, BKR5E-11, BKR5EIX, BKR5EK, BKR5ES, BKR5ES-11, BKR5EYA, BKR5EYA-11, BKR6EKB-11, FR4, FR45, FR5; Replaces Autolite 3924, 3926, 5224, AP3924, APP3924, AP5224, APP5224, XP3924, XP5224, XST3924, ZXT3926 Lifetime guarantee