In Figure 9 a female identification tag is formed by overmoulding between mould parts (8, 9) a base section (1) which will include inwardly directed projections or fingers (4) to retain in use the head of a male tag and may include an RFID coil (6). As the mould parts (8,9) separate, the core (10) can start to eject, moving through the flexible opening (13) formed at the top of the soft boss (12) of the tag. Subsequently, a hard insert can close off the opening (13) in providing tamperproofing. The core (10) can be caused to rotate as it moves through the flexible opening (13) in order to break any bond between the plastics material and the core (10).