Abstract: A cable underpinning usable, for example in spark-plug assemblies, comprises a pipe stub connected to a spark-plug housing and a deformable sleeve provided with a plurality of longitudinal slits or apertures. The pipe stub has a first inner cylindrical surface connected by means of a frusto-conical surface to a second inner cylindrical surface which is smaller in diameter than the surface of the sleeve when the same is in an unstressed or uncompressed state, the second cylindrical surface being provided with a plurality of sharp-edged recesses. Upon the passing of the cable through the sleeve and the force-fit insertion of the sleeve into the pipe stub, bulges are formed in the sleeve which protrude into the recesses, thereby preventing rotary and axial motion of the sleeve relative to the pipe stub. The flexible outer layer of the cable also bulges into the slits, which bulging locks the cable to the sleeve.