Within 18 months, Braun shavers cut an average of 6,000,000 hairs. That comes with some gradual wear to the cutting parts, which can lead to a less comfortable shave. That's why Braun recommends changing your shaver's foil & cutter block every 18 months to get your shaver back to its best. Take care of your shaver, and it'll take care of you. Please note that this product is designed for use with a BS 4573 shaver socket.