The Spectra Backflow Protector is a replacement protector for the Spectra M1 Double Rechargeable Breast Pump and Spectra S1 Hospital Grade Double Rechargeable Breast Pump. Each item consists of one backflow protector, so if you need to replace both protectors on your double pump, you will need to purchase two Spectra Backflow Protectors. (Spare Backflow Protectors specifically for the Handsfree Set are also available.)