Propellers are marked either "C" (for 'clockwise') or "A" (for 'anticlockwise'). The propellers should be mounted as follows, motor 1: "C", motor 2: "A", motor 3: "C", motor 4: "A". This kit includes 4 propellers (2 "C" and 2 "A") and 8 circlips.
For easy mounting, a special circlip tool is available in the "mounting tools kit" to easily insert and remove the circlips which connect the propellers and the gears to the shaft.