The reduction coefficients appearing in the decomposition of direct products of irreducible representations 4×4, 4×5, 4×10, 5×5 of the group B2 are calculated. Some examples of their application to the strong interaction symmetry of elementary particles are given: the relations between various scattering cross sections and the mass relations for low-dimensional irreducible representations are derived, and the assignment and decay modes of resonant states and the R-inverse invariance are discussed.