  Asteroid surfaces are subjected to mechanical weathering processes that
result in the development and evolution of regolith. Two proposed
mechanisms--impact bombardment and thermal fatigue--have been proposed as
viable and dominant weathering processes. Previously, we compiled and estimated
thermal inertias of several hundred asteroids (mostly in the main-belt) for
which we determined dependencies on temperature, diameter, and rotation period.
In this work, we estimate grain sizes of asteroid regoliths from this large
thermal inertia dataset using thermal conductivity models. Following our
previous work we perform multi-variate linear model fits to the grain size
dataset and quantify its dependency on diameter and rotation period. We find
that the best-fit model fit indicates that asteroid grain sizes are inversely
dependent on object size for <10 km asteroids and exhibits no relationship
above this size cutoff. Rotation period and grain size show a positive
relationship when the rotation period is greater than ~5 hr, and an inverse
relationship below this rotation period. We conclude that both impact
weathering and thermal fatigue are significant regolith evolution mechanisms.
Furthermore, we run post-hoc t-tests between spectral groups to identify
compositional differences among our asteroid set. Notably, suspected
metal-rich, M-type and E-type asteroids have larger than expected grain sizes,
and P-types have distinctly smaller grains than other groups
