The 1-Piece Standard Breastshield is "1-Piece" because it does NOT break into two pieces like the PersonalFit Breastshields (which come with the Pump-in-Style Advanced Breastpumps) or the SoftFit Breastshields. Think of it this way: the PersonalFit and SoftFit Breastshield must be used with PersonalFit Breastshield Connectors, a distinct replacement part which is sold separately. In contrast, the Standard 1-Piece Breastshield does not need to be used with a separate connector because the connector is part of the breastshield.
If you are using a Pump In Style or a Pump In Style Advanced Breastpump, you have three options: 1. Use a PersonalFit Breastshield with the PersonalFit Breastshield Connector, 2. Use a SoftFit Breastshield with a PersonalFit Breastshield Connector, or 3. Use a 1-Piece Standard Breastshield alone.
If you are using a Freestyle Breastpump, you can use the PersonalFit Breastshields with the Freestyle's pump body connector, OR the SoftFit Breastshields with the Freestyle's pump body connector, but you CANNOT use the 1-Piece Standard Breastshield.