MSD designed these firewall feed-thrus to prevent voltage leaks in passenger compartment mounted coil applications. Made from Rynite and nylon, they provide a 1/2 in. of insulation to ensure that the coil's spark reaches the distributor. They mount in a 1 in. diameter hole directly to the firewall and have high tension towers on each side, connected through a brass rod for full spark transfer. Available in red and a black/red combination.