A full 10.4mm in diameter! 409 Pro Race Wires are constructed from three layers of silicone and feature 102,000 volts dielectric strength. Designed around an 8mm 100% silicone ignition wire, then a tightly woven heat-treated fiberglass braid is applied over the inner 8mm core. Then a .409" diameter silicone jacket is extruded on top. This creates a permanent bond between all layers to prevent loose bulky sleeving that can collect moisture and other unwanted environment particles. The 409 Pro Race Wires feature a spiro-wound center conductor that can be used with most high performance ignition systems and protects against RFI (radio frequency interference) which can interfere with electronic ignitions, computer systems, and the vehicles radio.