to the axis of the storage drum the unwinding brake further has a braking component supported on the counter braking surface axially counter to the direction of yarn unwinding so as to produce spring action and having a coaxial braking surface also continuous in the peripheral direction the yarn feeder also has a mounting for the braking component and a pneumatic brake opening device which has a pressure chamber with a pneumatically loadable axially movable boundary wall the boundary wall is connected to the braking component so as to transmit movement at least in the direction of movement thereof counter to the action of the spring when the boundary wall is pressurised by excess pressure or a vacuum the braking component can be moved axially into a threading position in which the braking surface is lifted from the counter braking surface application_number US 6507598 A description a yam feeding device f according to fig1 for instance a yam storing and feeding device for projectile or gripper weaving machines of which only the free end part 3 of a storage drum t is shown as well as an extension arm 1 fixed onto the housing has a free end of the storage drum t provided with an output brake a which is designed as a coaxial disc brake the storage drum t has a withdrawal edge region 2 for the yam not shown and a yam brake b which cooperates in said region with the.