4DCopter &ldquo;Fly it, Love it!&rdquo; &trade;: X-Drone Nano 2.0 - &ldquo;Beautiful Design and Durable&rdquo;- 3 sets of Propellers (Total 12 propellers) You will receive 3 sets of propeller (3x4 propellers = total 12 propellers), each set contain two A type and two B Type . Please, be careful to replace propellers in the correct position. Each Propeller has printed the marks A1 , A2 , B1 and B2 to help you replace each propeller in its correct rotor. Warning1: Each rotor in the X-Drone Nano 2.0 rotates either clockwise or anti-clockwise to sustain flight. If you misplace a propeller , the drone will drop when you command to rise and vice versa , creating an impossible condition for X-Drone Nano 2.0 to fly. Warning2: If propeller are not properly replaced, rotors might be permanently damaged in its attempt to balance the X-Drone Nano 2.0