Reusable Breast Pump Flange Inserts: Designed to help optimize comfort and output for moms who measure smaller than 21mm, Willow Breast Pump Sizing Inserts in 15mm offers the pumping convenience you deserve Comfortable, Silicone Design: Flexible, BPA free silicone provides a snug, secure fit; Dishwasher safe, flange inserts for Willow Breast Pump are easy to clean; Clear color provides easy nipple visibility Compatible with Any Breast Pump: Pair with 24mm breast pump flanges and reusable containers; Keep a spare set on hand to minimize washing between hands free pumping sessions Find Your Perfect Fit: Breast pump inserts are available in 5 sizes: 13mm, 15mm, 17mm, 19mm and 21mm; Reference Willow's size chart to determine your size for an optimal pumping experience Trusted and True: We recommend replacing breast pump flange inserts every 3 months for optimal performance; Join the 300,000 moms who have brought Willow into their homes and lives