Contains 6 sealing caps or travel caps; compatible with Avent Natural Polypropylene bottles, Avent Natural Glass bottle, Avent Classic bottles and Maymom wide-neck bottles. Each cap contains 1 silicone sealing ring to prevent leaking. NOTE: if you use it with spectra bottles, DO NOT over tighten it. In this case, it will leak. One solid piece design. Replace Avent Natrual Screw Ring, and sealing disc. It also can replace Avent Classic Screw Ring (or nipple collar). Fewer parts to clean and easy to store. The sealing ring can be easily removed for cleaning. The thread of the cap can hold the sealing ring in place. It is unlikely for the ring to drop out of the cap unless removed by fingers. Can be used within temperature of - 10~110 deg C. Can be sanitized with water steam or boiling water; Dishwasher top rack safe (note: remove the sealing before putting it in the dishwasher). Microwave oven safe. Made from BPA free and DEHP free material. Comply with EU Commission Regulation (EU) No 10/2011 for plastic materials that intended to come into contact with food. US FDA compliant for food contacts. Every batch is tested by independent labs for quality and safety. After market product made by Maymom to fit Avent bottles. Please see the photo of the listing for comp ability.