  Quarks, leptons and heavy vector bosons are suggested to be composed of
stable spin-1/2 preons, existing in three flavours, combined according to
simple rules. Straightforward consequences of an SU(3) preon-flavour symmetry
are the conservation of three lepton numbers, oscillations and decays between
some neutrinos, and the mixing of the d and s quarks, as well as of the vector
fields W^0 and B^0. We find a relation between the Cabibbo and Weinberg mixing
angles, and predict new (heavy) leptons, quarks and vector bosons, some of
which might be observable at the Fermilab Tevatron and the future CERN LHC. A
heavy neutrino might even be visible in existing data from the CERN LEP
facility.
