# Flange sizes for Willow breast pumps Which flange sizes are offered for Willow breast pumps? Willow Pump Willow Go® Flange Set \(2\-pack\): Sold in three flange sizes: 21mm, 24mm and 27mm Willow Pump Willow Sync Flange Set 24mm \(2\-pack\): The flanges are 24mm\. Willow Pump Willow Sizing Insert Set: Sizes offered are 13mm, 15mm, 17mm, 19mm, 21mm and 27mm\. Willow Pump Breast Pump Sizing Kit: The kit provides a wide range of inserts to find the right breast pump flange fit for comfortable pumping and milk output\. ### 1. [Willow Pump Willow Go® Flange Set \(2\-pack\)](/products/ucp/onewillow-com/6705010081885) (sold by onewillow\.com) Sold in three flange sizes: 21mm, 24mm and 27mm - Sizes: Sold in three flange sizes: 21mm, 24mm and 27mm (listing) - Pack size: Sold as a 2\-pack (listing) - Notes: 24mm flanges fit sizing inserts for those measuring smaller than 21mm (listing) - SKU: - ### 2. [Willow Pump Willow Sync Flange Set 24mm \(2\-pack\)](/products/ucp/onewillow-com/7967832408157) (sold by onewillow\.com) The flanges are 24mm\. - Sizes: The flanges are 24mm\. (listing) - Pack size: Sold as a 2\-pack\. (listing) - Notes: Designed for Willow Sync pumps\. (listing) - SKU: The SKU is PF2435\. (listing) ### 3. [Willow Pump Willow Sizing Insert Set](/products/ucp/onewillow-com/6552686755933) (sold by onewillow\.com) Sizes offered are 13mm, 15mm, 17mm, 19mm, 21mm and 27mm\. - Sizes: Sizes offered are 13mm, 15mm, 17mm, 19mm, 21mm and 27mm\. (listing) - Pack size: The sizing inserts come as a 2\-pack\. (listing) - Notes: They are designed for the perfect fit and performance with Willow and make pumping more comfortable for mamas with smaller flange sizes\. (listing) - SKU: Each size has its own SKU, for example SZ1385 for 13mm and S827 for 27mm\. (listing) ### 4. [Willow Pump Breast Pump Sizing Kit](/products/ucp/onewillow-com/8010761175133) (sold by onewillow\.com) The kit provides a wide range of inserts to find the right breast pump flange fit for comfortable pumping and milk output\. - Sizes: - - Pack size: - - Notes: The kit provides a wide range of inserts to find the right breast pump flange fit for comfortable pumping and milk output\. (listing) - SKU: The kit's SKU is USK110\. (listing) Every value in the table is a fact RoboTrunk checked, linked to the page it came from\. A dash means no checked fact fills that cell\. Prices and stock change, so this page prints neither: each product name links to its RoboTrunk page, which shows them live\. Written 2026-10-11T19:02:49.643Z. This page is published by RoboTrunk, a store built for shopping agents. The store named on this page sells the product and ships it. RoboTrunk is not the seller and never holds the money. Buying works in one path. RoboTrunk's tools prepare a checkout at that store, then hand back a short-lived link. The person approves the total; once RoboTrunk has checked the store's total against it, the person is given the checkout link to tap in their own browser, or, if the person prefers and gives permission, their agent may open the link and finish there, and payment always happens on the store's own checkout page. RoboTrunk never takes the payment or sees a card. Where the rest of this site is: - /agent/story.md is what RoboTrunk is and how it works, in full. - /agent/tools.json is every tool, its arguments and its answers. - /agent/merchants is every store you can buy from through RoboTrunk. - /products/ucp is every store's indexed products. - /products/search is one search across every store, in plain words. - [What RoboTrunk is](/agent/story.md) - [The tools and how to call them](/agent/tools.json) - [The stores you can buy from](/agent/merchants) - [Every store's products](/products/ucp) - [Search every store at once](/products/search)