  We discuss weakly bound states of a few-fermion system having spin-isospin
symmetry. This corresponds to the nuclear physics case in which the singlet,
$a_0$, and triplet, $a_1$, $n-p$ scattering lengths are large with respect to
the range of the nuclear interaction. The ratio of the two is about
$a_0/a_1\approx-4.31$. This value defines a plane in which $a_0$ and $a_1$ can
be varied up to the unitary limit, $1/a_0=0$ and $1/a_1=0$, maintaining its
ratio fixed. Using a spin dependant potential model we estimate the
three-nucleon binding energy along that plane. This analysis can be considered
an extension of the Efimov plot for three bosons to the case of three
$1/2$-spin-isospin fermions.
