The diaphragm is the round, plastic assembly that attaches to the top of the breast shield to allow for closed-system pumping. This assembly is affixed to the breast shield on one side and the tubing that goes to the motor of the pump on the other side. These diaphragms are compatible with the Luna Breast Pump. The diaphragm creates a closed system, serving as a barrier to prevent milk from getting into the tubing or the pump. This is crucial in preventing contamination and the buildup of mildew or bacteria. What's Included: Diaphragm Top (X2), Diaphragm Bottom (X2), Diaphragm Membrane (X2)