Probably the most widely known and researched property of carbon nanotubes is their strength. To date, they are the strongest and stiffest material yet discovered in terms of tensile strength (the stress or pressure of tension the material can endure) and elastic modulus (or Young's Modulus, the ratio of tensile to stress to elastic deformation) respectively. In 2000, stress testing of MWNTs revealed a tensile strength of 63 gigapascals (GPa). By real-world approximation, this would be akin to hanging two average pickup trucks from a rope the thickness of a standard paper clip.
Unfortunately, much like a rope, nanotubes are not nearly as strong under compression, torsion (twisting) or bending stress and will tend to buckle because of their hollow structures and high aspect ratios.