Hegen's breast pump adapters allow you to express directly into Hegen bottles. Express, store, and feed within a single container with no wasteful transfer of milk necessary! Simply swap adapters with our storage lids or feeding collars to store or feed. Hegen breast pump adapters are compatible with most leading electric and manual breast pumps on the market. Make every drop count with Hegen. Hegen's breast pump adapters are not compatible with the Medela Flex and Pigeon Go Mini pumps. Hegen PCTO Standard Neck Adapters have a diameter of 3.5cm and will allow you to adapt your breast pump to Hegen bottles. Do note that different breast pump bodies/shields/flanges differ in opening size and you should check and match accordingly.