High performance, 40,000 volt ignition coils from Pertronix.  Very good quality and long term durability.  Available in either black or chrome finishes.
1.5ohm primary resistance coils are use for 6 and 8 cylinder cars with high performance ignition systems.  Use a 1.5ohm coil with the 123 distributor on an inline-6 engine (GT6, TR250, TR6).
3.0ohm primary resistance coils are for use with all 4 cylinder ignition systems and stock style 6 cylinder ignition systems.