We stock a few spare parts for the Medela bottles, as you might need some extras. This is the Screw Lid which is used hold a teat in place while you're feeding baby. Simply pull the teat upwards through the underside of this yellow piece, and the ridge at the wide end of your teat will hold it in place.
This screw top is not compatible with Medela Calma, nor Avent.
Teat not included but just used for photograph on this webpage.