Ouasi stoichiometric model SiC mono-filaments (C/Si atomic ratio approximate to 1.02) with still some free carbon (approximate to 3 mol %) and residual oxygen have been produced from a novel copolymer precursor, itself prepared from methylphenyldichlorosilane and 2,4-dichloro-2,4-disilapentane. The continuous green fibre was melt spun at 230 degrees C, cured by electron-beam irradiation, and pyrolysed under argon at temperatures, T-p, in the range 1000-1600 degrees C. The fibre remained nanocrystalline at high temperature with the SIC grain size growing from 1.5 nm to 7.3 nm when T-p was raised from 1400 degrees C to 1600 degrees C. Its Young’s modulus continuously increased as T-p was raised (with E = 320 GPa for Tp = 1400 degrees C), whereas its tensile strength at room temperature underwent a maximum for T-p = 1200 degrees C (sigma(R) approximate to 1850 MPa for L = 10 mm and d approximate to 20 mu m).