APC slow fly propellers are among the most efficient and quietest RC propellers for low RPM electric flight applications. All propeller sizes are quoted in inches. Use Slow-fly type propellers with all AXi 22xx series motors.
The maximum RPM for these propellers can be calculated using the following formula: 65,000 / prop diameter in inches
For example the 10"x4.7" tractor/pusher propellers have a maximum RPM of 6,500 revs.