Secondary electrons with kinetic energy E>8 eV from Fe, Co, and Ni have recently been shown to reflect the expected spin polarization P of the average of the conduction bands of these metals. However, as the threshold value E=0 is approached, the secondary electron polarization sharply increases for each of these metals. It is pointed out that the values for P at E≊0 for secondary electrons agrees very well with the values of P for tunneling electrons. The tunnel current is contributed mainly by a small number of highly mobile electrons from s-d hybridized bands, rather than by the more localized d electrons which contribute most of the magnetic moment. For these bands the sign and approximate magnitude of P are correctly predicted from the known band structure. Inelastic processes that have been suggested to explain the increase in P at E≊0 for secondary electrons cannot apply to elastic tunneling at EF. It is proposed the values of P of secondary electrons for E≊0 reflect the polarization of the s-d bands which contribute to the tunneling current.