The invention relates to a connection device comprising —a line portion (10) having, at its end, a radially outwardly projecting abutment flange (14) for butting against a corresponding abutment flange of a further line portion which is to be coupled to the line portion (10), and—a ring-segment chain (42, 22, 38) comprising a plurality of ring segments (22, 38) connected to one another in a pivotable manner in a common ring plane, wherein the ring-segment ends which formed the chain ends can be latched to one another to give a ring-form connection clamp (42). The invention is distinguished in that the line portion is designed in the form of a tubular connection stub (10) with first thread means (16) spaced apart axially from the abutment surface (141) of its abutment flange (14), and in that each ring segment (22, 38) has a radially inwardly projecting clamping flange (24) and second thread means (26), which are spaced apart axially from said clamping flange and correspond with the first thread means (16).