The BPMR6A is a commonly stocked spark plug as it is the number one chainsaw spark plug.

The BPMR7F is the more common large gas model engine spark plug and has the same reach and threads as the "A" plug. The "F" plug is tapered seat and is used where the "A" was used interchangeably.

The running characteristics are the same with either spark plug.

The BPMR7F requires a different cap than the "A" plug because it is smaller externally. You will see the different caps advertised where people sell universal ignition systems.