  As the closest open cluster to the Sun, the Hyades is an important benchmark
for many stellar properties, but its members are also scattered widely over the
sky. Previous studies of stellar rotation in the Hyades relied on targeted
observations of single stars or data from shallower all-sky variability
surveys. The re-purposed Kepler mission, K2, is the first opportunity to
measure rotation periods ($P_{rot}$) for many Hyads simultaneously while also
being sensitive to fully convective M dwarf members. We analyze K2 data for 65
Hyads and present $P_{rot}$ values for 48. Thirty-seven of these are new
measurements, including the first $P_{rot}$ measurements for fully convective
Hyads. For nine of the 11 stars with $P_{rot}$ in the literature and this work,
the measurements are consistent; we attribute the two discrepant cases to spot
evolution. Nearly all stars with masses $\le0.3M_\odot$ are rapidly rotating,
indicating a change in rotation properties at the boundary to full convection.
When confirmed and candidate binaries are removed from the mass-period plane,
only three rapid rotators with masses $\ge0.3M_\odot$ remain. This is in
contrast to previous results showing that the single-valued mass-period
sequence for $\approx$600 Myr-old stars ends at $\approx0.65M_\odot$ when
binaries are included. We also find that models of rotational evolution predict
faster rotation than is actually observed at $\approx$600 Myrs for stars
$\le0.9M_\odot$. The dearth of single rapid rotators more massive than
$\approx0.3M_\odot$ indicates that magnetic braking is more efficient than
previously thought, and that age-rotation studies must account for
multiplicity.
