The invention relates to a disk brake (B) for a thread (Y). Said disk brake has a run-in disk (E) which can be pressed against a stationary run-out disk (A) under the influence of a magnet (M), with a circular braking surface (2). The run-out disk (A) has a central run-out opening (16) for the thread (Y), which is braked between the braking surfaces (2, 14) which are oriented radially in relation to the brake axis (X). The run-in disk (E) is held in the nose area of a storage drum (D) of a thread storage device (F), in a manner that allows the disk to wobble, while the magnet (M) and the run-out disk (A) are held in a stationary support (S). The invention provides that the run-in disk consists of magnetic material and the magnet (M) acts on the run-in disk (E) magnetically through the run-out disk (A), so that the braking force that is exerted on the thread between the braking surfaces can be adjusted and varied.