Abstract: A resistivity measuring head comprising a body portion and a replaceable nose portion. The body portion contains a plurality of spring-loaded pins located for axial movement in aligned plain openings in a pair of spaced guide plates, and the nose portion contains a number of probes, one for each pin, each precisely mounted in a pair of precisely aligned jewel bearings. The pins bear against one end of the probes for applying an axial working force thereto. Electrical connections are made to the probes either through the intermediacy of the pins or through a plug and socket arrangement wherein the probes are connected to plug pins carried by the nose piece and adapted for engagement with sockets in the body portion.