  The contact values $g(\sigma,\sigma')$ of the radial distribution functions
of a fluid of (additive) hard spheres with a given size distribution
$f(\sigma)$ are considered. A ``universality'' assumption is introduced,
according to which, at a given packing fraction $\eta$,
$g(\sigma,\sigma')=G(z(\sigma,\sigma'))$, where $G$ is a common function
independent of the number of components (either finite or infinite) and
$z(\sigma,\sigma')=[2 \sigma \sigma'/(\sigma+\sigma')]\mu_2/\mu_3$ is a
dimensionless parameter, $\mu_n$ being the $n$-th moment of the diameter
distribution. A cubic form proposal for the $z$-dependence of $G$ is made and
known exact consistency conditions for the point particle and equal size
limits, as well as between two different routes to compute the pressure of the
system in the presence of a hard wall, are used to express $G(z)$ in terms of
the radial distribution at contact of the one-component system. For
polydisperse systems we compare the contact values of the wall-particle
correlation function and the compressibility factor with those obtained from
recent Monte Carlo simulations.
