A yarn feeder (F) including a holding device (H) for holding a yarn braking body in an extension arm (2, 2a) of a housing, a support body (6a) for a holder (5) of the yarn braking body (4) and a moving drive including a cylindrical piston (6b) which is movable in a cylinder (7) to move the yarn braking body (4) between a braking position and a gap position relative to a storage body (3) of the yarn feeder (F). The piston (6b) is arranged as an integrated guide element of the support body (6a) on the support body (6a). At least one guide nose (9) which engages into a guide track (10) fixed onto the extension arm is provided as a rotation preventing member on the piston and/or on the support body at a transverse distance from the piston axis (X).