  Transition metal impurities will yield zero bias anomalies in the conductance
of well contacted metallic carbon nanotubes, but Kondo temperatures and
geometry dependences have not been anticipated so far. Applying the density
functional plus numerical renormalization group approach of Lucignano
\textit{et al.} to Co and Fe impurities in (4,4) and (8,8) nanotubes, we
discover a huge difference of behaviour between outside versus inside
adsorption of the impurity. The predicted Kondo temperatures and zero bias
anomalies, tiny outside the nanotube, turn large and strongly radius dependent
inside, owing to a change of symmetry of the magnetic orbital. Observation of
this Kondo effect should open the way to a host of future experiments.
