Bounds on Radii and Magnetic Dipole Moments of Quarks and Leptons from   LEP, SLC and HERA
  Leptons, quarks and gauge bosons are assumed to be pointlike particles in the Standard Model. Stringent bounds on the radii of quarks and leptons and their weak anomalous magnetic moments can be derived from the high-precision measurements at LEP and SLC. We find a model-independent bound of $R\lsim 10^{-17}cm$ for quark and lepton radii. HERA will provide complementary information on the electromagnetic static properties of the quarks and the parameters of the charged quark currents. 
G. K"opp, D. Schaile, M. Spira, and P.M. Zerwas