H-D #4, one range colder. M18 X 1.5 threaded.  1/2" (12.7mm) short reach. Used with 24mm spark plug socket. This D14 (H-D #4) is one range colder (runs less hot/removes heat faster) than the standard D16 (H-D #3) spark plug. This D16 is available as MCS 931600. The cooler running proporties make this D14 is better suited for high speed riding, as found in extended highway use. Spark plug is copper-core center electrode and comes with the patented Ultraseal™ coated shell, to help keep the spark plug corrosion free for a longer period of time.