Single walled carbon nanotubes can be used as nanoscale reaction chambers for producing smaller nanotubes within the host tube from encapsulated fullerenes by annealing. The diameter of the host outer tube restricts the diameter of the inner tube due to van der Waals interactions, but not chirality; however, only a few chiralities are allowed for any given outer tube diameter. It is possible that inner tubes with different chiralities – or the same chirality but left- and right-handedness– can start to grow in different places at the same time. A straight junction occurs at the connection of these two tubes. The geometry of different kinds of junctions containing pentagon and heptagon defects was optimized by density functional theory. The effect of the localized states on the electronic band structure was investigated. Geometry of our (6,4) nanobamboo from two points of view. The pentagon and heptagon defects are highlighted.