This part of ISO11093 specifies a method for the determination, by the three-point method, of the flexural modulus of cylindrical paper and board cores which meet the following criteria: — internal diameter: 50mm to 350mm; — minimum wall thickness: 0,05×internal diameter, but not less than 10,0mm; — minimum length of core: 10×internal diameter, but not less than 1000mm. If the flexural modulus has to be used for the calculation of a paper core’s natural frequency, ISO11093-8[2] applies instead of this International Standard.