Braun 31B Replacement Foil and Cutter Cassette Multi Black BLS The Braun 31B Replacement Foil and Cutter Cassette Multi Black BLS is a high-quality replacement part designed for Braun Series 3 shavers. It ensures a close and comfortable shave by combining advanced foil technology with a durable cutter cassette. This replacement head is easy to install and helps maintain the peak performance of your shaver, delivering efficient results every time. Braun recommends replacing the foil and cutter cassette every 18 months for optimal shaving performance.