In this paper, a new type of screw propeller for capsule endoscopes is introduced whose rotation motion is enforced by magnetic forces between an armature magnet inside the capsule and an external rotating permanent magnet working like an AC stator. The screw propeller consists of flexible threads attached on the capsule body. The spiral angle of the flexible threads switches automatically due to the friction force between intestine wall and the capsule body when the rotating direction of the capsule body is reversed. Therefore, the moving direction of the capsule is independent of the rotating direction of the capsule body. This will help the capsule advance especially in curved tracts by changing its effective thread angle for reduction of friction torque. In order to investigate main parameters that influence the performance of the new screw propeller, we evaluated the speed of the capsule with various shapes and sizes of the flexible threads, changing the parameters such as rotational speed of the external permanent magnet, distance between the external magnet and the armature magnet inside the capsule, and viscosity of lubrication oil in artificial intestine tract. The speed of the capsule with the flexible screw propeller was mainly dependent on the shape of threads. Also, the distance between the magnets highly influenced the speed of the capsule since thrust force of the capsule was dependent on it. On the contrary, rotational speed and oil viscosity insignificantly contributed to the speed of the capsule. Especially in curved tracts, the effective thread angle of the screw propeller which could be changed by its rotation direction played a great role in advancing the capsule efficiently.