Abstract: A security seal having a locking body and a thread having a first end attached to the body and a second free end, the body having an entry opening for insertion of the second end of the thread and further, inside it a locking device that permits passage of the second end of the thread in the insertion direction and prevents withdrawal of the thread in the opposite direction. The locking device is in the form of wedges (14) to open and close the passage for the thread (2). The wedges (6) are linked to the rest of the body by spring connection portions (20) and molded together with the body in order to facilitate its manufacture.