Single fire super coil for aftermarket ignition Big Twin and Sportster, single fire, 3 OHM. Designed for single spark plug per head applications. Can be used with aftermarket ignition systems that incorporate a mechanical advance. Fits Big Twin and Sportster with aftermarket single fire ignitions that require a 3 OHM coil. Will not fit models with OEM single fire ignitions such as Electronic Fuel Injection, Twin Cam or 1200 Sportster