Spectra Baby Premium Accessory Kit includes: ONE of each of the following, Wide Neck Flange 28mm, Backflow Protector, Tubing and White Duckbill Valve, 5 oz (160 ml) Wide Neck Bottle with Bottle Cap, Collar ring and Sealing Disk. If double pumping, please buy two ($57.99). If double pumping, please buy two sets. Parts are designed for use with the Spectra S2, S1, DEW 350, 9 Plus, and M1 breast pumps. This wide neck breast shield is also compatible with Spectra wide neck bottles. If double pumping, please buy two. 2 sizes available: Medium--24mm, Large--28mm. Discounts for higher quantities.