Abstract We have investigated the properties of purely metallic carbon nanotube systems made of a nanometer-size metallic island connected to another two metallic carbon nanotubes by means of topological defects. These structures present discrete energy levels, thus behaving as metallic quantum dots. When there is a symmetry gap between the matched tubes around the Fermi energy, the states are strongly localized in the central metallic section and completely uncoupled from the external nanotubes. Interestingly, we also find discrete states in structures made of metallic nanotubes without a common symmetry. In this case the states are actually resonances coupled to the leads continua.