No other element in the periodic table bonds to itself in an extended network with the strength of the carbon-carbon bond. This special nature of carbon, combined with the molecular perfection of single-walled nanotubes endows these nanotubes with exceptional material properties, such as very high electrical and thermal conductivity, strength, stiffness, and toughness. As a result, single-walled carbon nanotubes (SWCNTs) are the strongest material known to science. SWCNTs potentially can add incredible strength, stiffness and electrical conductivity to all kinds of composite materials. Unfortunately, they are always held together in rope form due to their extremely small dimension and van der Waals attraction and their strength can neither be exploited nor measured. However, if several SWCNTs are concentrically nested in a confined space, the sliding issue can be resolved and the SWCNTs may share the applied tensile load to realize nanometer-scale materials remarkably stronger than the individual SWCNTs.