  We study a combination of amplitudes for neutrino scattering that can isolate
a (gauge-invariant) difference of chirality-preserving neutrino electroweak
radii for $\nu_\mu$ and $\nu_\tau$. This involves both photon and $Z_\mu$
exchange contributions. It is shown that the construction singles out the
contributions of the hypercharge gauge field $B_{\mu}$ in the standard model.
We comment on how gauge-dependent terms from the charge radii cancel with other
terms in the relative electroweak radii defined.
