Abstract: A snap-on tubular coupling for joining tubular conduit members of the type having axially extending grooves for guiding geophysical instruments. The coupling comprises an unthreaded sleeve slotted to provide outwardly deflectable segments at one or both ends to snap onto ends of the conduct members to be joined. An internal circumferential rib on the sleeve engages a circumferential groove on the conduit. A cylindrical key or button on the casing engages a slot in the end of the coupling to ensure that the longitudinal grooves of the conduit members are in alignment.