Electrically conductive columns of intertwined carbon nanotubes embedded in a mass of material flexible, resilient electrically insulating material can be used as electrically conductive contact probes. The columns can extend between opposing sides of the mass of material. Terminals of a wiring substrate can extend into the columns and be electrically connected to an electrical interface to a tester that controls testing of a device under test. A pair of physically interlocked structures can coupling the mass of material to the wiring substrate. The pair can include a receptacle and a protrusion.