A tool for making a plug connection between a plastic tube and a plastic case for electrical conductors has a cutting head which is designed to encircle the shell of a tube and which can be turned relatively to the tube. Extending into the interior of the cutting head is a first knife for chamfering the end of the tube as well as a second knife, at a distance from the first, for cutting a fircone-shaped rib in the shell of the tube. The cutting head is firmly connected to one end of a bar-shaped handle, which is provided at its other end with a bore head for making a hole in the wall of the case. The bore head comprises a cutter on an end of a steel hollow cylinder connected at its other end to the handle and projecting out from its respective front end. A protective and centering plunger is slidable against the effect of a spring within the hollow cylinder coaxially with the handle, the plunger forming on its free end a pressure plate which, in the normal state of the tool, projects above the cutter on the hollow cylinder.