Electrical connectors comprising carbon nanotubes, at least one polymer, and a metallic electrical conductor are described. During and after assembly, the elastic engagement pieces elastically abut at least an outer surface of a tapered shank in a tool holder and deform slightly in a radial direction. Herewith, it provides functions of electronic purse and telecommunication value added service integration. Both types of diverging section are designed to reduce slipping and are connected to rear corners of the fastener-engaging cavity that are designed and positioned to avoid contact with the rear side corners of the fastener.