An observed deviation of the angular velocity of spoke features from the Keplerian value can yield the charge to mass ratio of spoke particles. Published observations of spoke motion are consistent with q/m in the neighborhood of -10 coul/kg. Since a lower llimit on q is one electronic charge, this value yields a lower limit to the size of spoke particles of about 10-2 &mgr;m. The criteria for electrostatically ejecting small particles from larger parent bodies indicate an upper limit of about 103 m for the parent bodies. Stability of the grains against electrostatic disruption or field emission yields an upper limit of ~3 &mgr;m for the spoke particle size and leads to the conclusion that the spoke particles must consist of material which is stronger than loose dust balls.