  We report spectroscopic observations of vB 120 (HD 30712), a 5.7 yr
astrometric-spectroscopic binary system in the Hyades cluster. We combine our
radial velocities with others from the literature, and with existing speckle
interferometry measurements, to derive an improved 3D orbit for the system. We
infer component masses of M1 = 1.065 +/- 0.018 MSun and M2 = 1.008 +/- 0.016
MSun, and an orbital parallax of 21.86 +/- 0.15 mas, which we show to be more
accurate than the parallax from Gaia DR3. This is the ninth binary or multiple
system in the Hyades with dynamical mass determinations, and one of the
examples with the highest precision. An analysis of the spectral energy
distribution yields the absolute radii of the stars, R1 = 0.968 +/- 0.012 RSun
and R2 = 0.878 +/- 0.013 RSun, and effective temperatures of 5656 +/- 56 K and
5489 +/- 60 K for the primary and secondary, respectively. A comparison of
these properties with the predictions of current stellar evolution models for
the known age and metallicity of the cluster shows only minor differences.
