Breast Shield Set to replace your original breast pump parts or to keep an extra set at work. If double pumping, please buy two. Spectra 20mm Breast Shield set is great for our Spectra pumps when needing replacement parts in a set. Spectra recommends replacing your parts every 3-6 months for optimal use. If you are needing a full set of replacement parts or want to have an extra set on hand for home or work this kit is for you and your S2, S1, 9 Plus or M1 pumps.