Abstract: A thread tightener has a hollow body (49) in which is arranged a thread channel (4), as well as a tightening body (10) which may be pressed against the outlet part (49) of the thread channel (4). The hollow body (40) contains a first hollow section (41) and a second hollow section (42) which is rotatively mounted on the first hollow section (41). The thread tightener further has a device (9) for controlling the force with which the tightening body (10) is pressed against the outlet surface (47) of the hollow body (40). This control device (9) has a two-armed lever (11). One of the urns (12) of said lever carries the tightening body (10). The other level arm (13) is coupled by a spring (19) to a slide (30) for adjusting the compression force of the tightening body (10). This slide (30) is coupled by a gear to the rotary hollow insert (42 ). This thread tightener allows the braking force to be very finely adjusted and may have very small dimensions.