This is the Evolution 12x4 Alpha 60 3-Blade Propeller. The Evolution Engines Alpha 60 three blade propeller was designed to fly at slow speed while maintaining excellent thrust for climb and aerobatic maneuvers. Engine sizes from 50 to 61 can easily spin this 12x4 three-blade propeller. This prop will control the top speed of your model within a 52 to 70 mph range, which is very practical for training purposes. However the high thrust at low speed is perfect for 3D flying in models designed for maneuvers at slow speed.