Do not use Nylon Propellers if the Velocity of the propeller tip exceeds 180 m/s. Maximum propeller RPM is then Governed by the diameter of the Propeller Tip Circle and can be calculated using the following Formula: Constant(SAFE VALUE)3438 (INCLUDING, LIMITING FACTOR): Diameter of the propeller in Meters. Taking a 28 cm Diameter propeller the FORMULA reads: 3438: 0.28=12.279 rpm in order to preserve the strength the water contents must stay trapped in the nylon material. For that reason they should be stored as cool and as moist as possible. Be careful when the propeller is rotating: Do not stay in the plane of the rotation level of the propeller! DO NOT USE ANY DAMAGED PROPELLERS! Some Propeller Manufacturers recommend dipping a nylon Propeller into lightly boiling water for no more than 2 minutes then allow too cool to room temperature gradually.