The product is a 20-piece set of vented 4.0 domes specifically designed for Phonak hearing aids, with a medium size of 0.43 inches (9mm). Made by the brand ZarEpsilonyx, these black domes are compatible with the Phonak Bolero™ Marvel model. These domes provide a secure and comfortable fit for daily use, ensuring optimal sound quality and security for the user's hearing.