This is THE prop for 120SR and brushless tail motors on the MCPx. 

 Note this is a Tractor prop, you will have to reverse the direction of the tail motor, or flip it in the mount. The shiny side of the blades should face to the right when looking from the back of your MCPx!

 Press fit onto a 1mm shaft, balancing is recommended. Weight is Approx. .38 grams.

 Please check the clearance between the prop and the main blades when using short booms and raised tail motor mounts.