Spiral wound inner core with 8mm silicone jacket. Compatible with both points and electronic H-D ignitions. This is a ''cut to required length'' universal spark plug wire set with 2 wires and 4 plug boots attached for dual plugged motors. Coil boots and terminals must be installed. Note: Compatible with all H-D electronic ignitions. For custom electronic ignitions; check the electronic module instruction manual to see if the module is compatible with Ferro-Spiral™ core wires. Note: Will not fit coil connection on stock single fire models like all Twin Cam; M8 and 98-03 XL 1200S models.