Permanent magnet external rotor (1) for an electric motor, comprising a cup-shaped body (2) provided with a bottom (20) and a side wall (21); at least one magnet (3), defining a plurality of poles and fixed inside said cup-shaped body (2); and a metal insert (4), defined by a helical spring fitted around the at least one magnet (3) which forms the closure of a magnetic circuit of the electric motor.