Size 15mm. Used only a few times until I realized they were too small for me. They fit my spectrum pump with a compatible momcozy adapter. Patented BabyMotion Flange is developed based on biomechanical studies of nursing babies. It compresses the nipple and areola during pumping to maximize milk expression, like a baby. BENEFITS Mimic Nursing - BabyMotion Flange transforms pumping into nursing, giving pumping a bit more the human touch. Stimulate Let-down - BabyMotion Flange compresses nipple and areola during pumping, which sends a signal to your brain to stimulate let-down and help release milk. Soft and Comfortable - BabyMotion Flange is soft and non-abrasive, which is way more comfortable than hard plastic flanges. Better Seal - BabyMotion Flange is soft and therefore moves with your breast while you pump to ensure a better seal, which makes breast massaging easier. Improved Privacy - BabyMotion Flange is semi-transparent and protects your privacy even if a family member or co-worker accidentally walks in on you while pumping. Wash fewer Parts - BabyMotion Flange's one-piece design allows you to wash less parts than traditional soft breast shield inserts. Potentially Increase Pumping Efficiency - Research has shown that adding a compression stimuli during pumping increases pumping efficiency. - Potentially Increase Production Research has shown that emptying your milk more during each pumping session will increase your production.