This part of ISO 11093 specifes a method for the determination, by the three-point method, of the fexural modulus of cylindrical paper and board cores which meet the following criteria:- internal diameter:50 mm to 350 mm;- minimum wall thickness:0,05 × internal diameter, but not less than 10,0 mm;- minimum length of core:10 × internal diameter, but not less than 1 000 mm.If the fexural modulus has to be used for the calculation of a paper core’s natural frequency, ISO 11093-8[2] applies instead of this International Standard.