Abstract: In a thread brake, which comprises at least one brake element (B) adapted to be moved relative to a counter brake element (B.sub.G), said brake elements acting on the thread in braking positions and being adapted to be displaced up to and into a threading position in which the thread can be moved undecelerated through the thread brake, and in the case of which a brake element adjustment device is provided, the threading position of the thread brake (F.sub.K, F.sub.L, F'.sub.L) can be established with the aid of a drive means (A) of said adjustment device, said thread brake having provided therein air guide surfaces (L), which, in the threading position, define an air guide passage used for automatic, pneumatic threading of the thread (Y) by means of a stream of air.