<span style="font-style: Normal;font-weight: bold;">100% Performance 1 Foil & Cutter Fits Series 1 shaver models. <ul start="1" style="list-style-type:disc"><li value="1"> Blades should be replaced every eighteen months. <li value="4"> For optimum performance, clean regularly. 11B Series 1 Within 18 months on average, a Braun shaver will cut an average of 6,000,000 hairs - equivalent to shaving an entire soccer field. In accomplish ing this substantial task, the cutting parts will gra dually wear out and your shave may become less close and comfortable. Therefore Braun recommends changing your shaver's foil & cutter block every 18 months to maintain your shaver's maximum performance.