This listing is for one breastshield insert. This piece fits INSIDE the standard (24mm) breastshield to make a smaller opening (21mm). This part is NOT a breastshield - it is only an insert. This part used to be included inside the breastshields in all new Pump In Style Original Breastpumps.
The 21mm size of the breastshield insert is the same size as the new PersonalFit small size breastshield.