The spark plug wiring used with ignition systems is a carbon impregnated cord conductor that is encased in either a 7 mm (9/32 in) or an 8 mm (5/16 in) silicone rubber jacket. The silicone jacket withstands very high temperatures. Silicone spark plug boots form a tight seal on the plug. The boot should be twisted a half turn before removing. Care should be used when connecting a timing light or other pick-up equipment. Do not force anything between the boot and the wiring, or through the silicone jacket. Connections should be made in parallel using an adapter. Do not pull on the wire to remove. Pull on the boot, or use a tool designed for this purpose.