A tag to be fixed to a connecting thread to a filter bag for infusion products has a flat body delimited by a perimeter edge; a first slit, starting from a first point of a side of the perimeter edge; a second slit and a third slit, starting from respective points of such side of the perimeter edge arranged on opposite sides with respect to the first starting point of the first slit. At least one of the second and third slits exhibits, starting from the respective starting point on said side, a progression and a development directed towards a point of a straight line in the plane of the body of the tag and perpendicular to said side at the first starting point of the first slit; the first slit, the second slit and the third slit being such as to enable passage there-through of a connecting thread, for fixing the tag to the thread.