Champion Spark Plug J12YC (2) 48-74 Big Twin

H-D 3-4. 14mm threaded, 1/2" (12.7mm) short reach. Used with 21mm spark plug socket. Copper-core center electrode. Spark plug comes with the patented Ultraseal™ coated shell, to help keep the spark plug body corrosion free and better looking for a longer period of time.