  Several low-mass eclipsing binary stars show larger than expected radii for
their measured mass, metallicity and age. One proposed mechanism for this
radius inflation involves inhibited internal convection and starspots caused by
strong magnetic fields. One particular eclipsing binary, T-Cyg1-12664, has
proven confounding to this scenario. \citet{Cakirli2013a} measured a radius for
the secondary component that is twice as large as model predictions for stars
with the same mass and age, but a primary mass that is consistent with
predictions. \citet[][]{Iglesias2017} independently measured the radii and
masses of the component stars and found that the radius of the secondary is not
in fact inflated with respect to models, but that the primary is, consistent
with the inhibited convection scenario. However, in their mass determinations,
\citet[][]{Iglesias2017} lacked independent radial velocity measurements for
the secondary component due to the star's faintness at optical wavelengths. The
secondary component is especially interesting as its purported mass is near the
transition from partially-convective to a fully-convective interior. In this
article we independently determined the masses and radii of the component stars
of T-Cyg1-12664 using archival {\it Kepler} data and radial velocity
measurements of both component stars obtained with IGRINS on the Discovery
Channel Telescope and NIRSPEC and HIRES on the Keck Telescopes. We show that
neither of the component stars is inflated with respect to models. Our results
are broadly consistent with modern stellar evolutionary models for
main-sequence M dwarf stars and do not require inhibited convection by magnetic
fields to account for the stellar radii.
