Braun Cassette 70's - 9000 Series Braun replacement foil & cutter blocks help to maintain your shaver's maximum performance. Within 18 months, your Braun shaver will cut an average of 6,000,000 hairs. In accomplishing this substantial task, the cutting parts will gradually wear out and your shave may become less close and comfortable. Therefore Braun recommends changing your shaver’s foil and cutter block every 18 months to maintain your shaver’s maximum performance. For a perfect shave every day. Braun's most advanced Optifoil with ergonomically sized holes cuts hair deeper than ever before - for perfect closeness that lasts longer.