  In the present investigation the model of preons and their composites is
constructed in the framework of the superstring-inspired flipped E_6\times
\tilde E_6 gauge group of symmetry which reveals a generalized dual symmetry.
We assume that preons are dyons, which in our model are confined by
hyper-magnetic strings - composite N = 1 supersymmetric non-Abelian flux tubes
created by the condensation of spreons near the Planck scale. We show that the
six types of strings having fluxes \Phi_n = n\Phi_0 (n = \pm 1,\pm 2,\pm 3)
produce three generations of composite quark-leptons and bosons. We give an
explanation of hierarchies of masses in the Standard Model. The following
values of masses obtained in our preonic model: m_t\approx 173 GeV, m_c\approx
1 GeV and m_u\approx 4 MeV, m_b \approx 4 GeV, m_s\approx 140 MeV and
m_d\approx 4 MeV, m_\tau\approx 2 GeV \quad and m_\mu \approx 100 MeV, are in
agreement with the experimentally known results. The following left-handed
neutrino masses are predicted: m_1\approx 1.3\times 10^{-3} eV, m_2\approx
9.2\times 10^{-3} eV, m_3\approx 5.0\times 10^{-2} eV - for direct hierarchy,
m_1\approx 0.73\times 10^{-2} eV, m_2\approx 7.4\times 10^{-2} eV, m_3\approx
5.5\times 10^{-2} eV - for inverted hierarchy.
