A knot-tying head adapted to form a knot with a filament around a cylindrical part, and wherein the knot-tying head includes a first body and a second body, wherein both bodies are configured such that when they are attached they form a hollow space between one another for receiving the part; wherein the first body and the second body include at least one conduit forming a path substantially around the hollow space, and the conduit being adapted to receive the filament, and at least one groove communicating the conduit with the hollow space along all or part of its path, the width of the groove being less than the width of the conduit and greater than the width of the filament used to form the knot.