Generally, nanotubes can be described with a vector or pair of indices — (n,m).   Nanotubes which have m = 0 are zigzag carbon nanotubes.   If n = m or the indices are equal to each other, the nanotube is of the armchair orientation.   Any other indices indicate that the nanotube is chiral.   Larger indices mean that the nanotube has more hexagonal units perpendicular to the axis.   For example, a (8,0) zigzag nanotube will have a smaller diameter than (10,0) nanotube.