threaded section 11 c respectively the preassembled clamping unit 8 is centered and held in the outer body 6 as a result of the clamping elements 9 a 9 b preloaded relative to one another by a spring the clamping screw 11 projecting slightly from the outer body 6 on both sides if a pipe 5 is pushed in this pipe 5 is clamped in place by the clamping unit 8 by turning the clamping screw 11 the clamping unit 8 being automatically centered relative to the pipe 5 the length of the clamping screw 11 is expediently dimensioned in such a way that its head 11 a is accommodated by the outer body 6 when the pipe 5 is clamped in place as a result of which visual monitoring of the assembly is made possible at the same time the clamping units 8 if need be may be additionally supported on the lateral shoulders of the sealing sleeve 1 the outer body 6 adjacent to the clamping unit 8 may in each case expediently carry a guide ring 15 at the end faces for the pipe to be inserted which guide ring 15 in this exemplary embodiment encloses the outer body 6 and can thus counteract buckling of the outer body 6 when the pipe 5 is clamped in place in the embodiment of fig4 to 6 the clamping elements 9 a 9 b may.