Abstract: The invention concerns a yarn brake (B) comprising a brake (L) electromagnetically stressed against a fixed braking surface (17), a housing (1) whereon the cover bearing the brake (L) is mounted such that it is capable of being lifted relative to the fixed braking surface (17), and at least an adjusting arbor (S) controlling the lifting movements of the cover, said arbor being mounted on the housing (S) in geometric association to the path of the yarn (W). The invention is characterised in that the cover is a flap cover (K) mounted so as to be capable of being lifted about the adjusting arbor (S) for completely clearing the braking zone (12) of the yarn tension device (B).