sheath 1 a reinforced flange or ring collar 9 which is able to rest in the region of the compression groove 7 against an annular shoulder face 10 of the connector to make the pullproof and watertight joint the connector 3 is radially deformed by compression applied to the portion of its length forming the pressed sleeve 4 and corresponding to the depth of engagement of the sheath 1 into the sleeve form connector such compression being in itself a known process through this compression the sheath 1 is firmly gripped between the internal backing sleeve 8 and the portion of the length of the connector which surrounds it i e the pressed sleeve 4 the original outer contour of the portion of the length of the connector 3 forming the pressed sleeve 4 prior to compression is indicated in fig1 at 4 39 upon radial compression the flexible sheath is radially deformed and is tightly gripped between the backing sleeve 8 and the pressed sleeve 4 but owing to the presence of the compression groove 7 in the region of the end of the inserted sheath 1 the deformation forces cannot be transmitted to the surmounting portion of the length of the connector 3 forming the coupling sleeve 5 as here the wall thickness of the sleeve form connector is significantly greater than in.