  Primordial black holes (PBHs) are an important tool in cosmology to probe the
primordial spectrum of small-scale curvature perturbations that reenter the
cosmological horizon during radiation domination epoch. We numerically solve
the evolution of spherically symmetric highly perturbed configurations to
clarify the criteria of PBHs formation using a wide class of curvature profiles
characterized by five parameters. It is shown that formation or non-formation
of PBHs is determined essentialy by only two master parameters.
