as we all know, out bush and inner bush, once the inner and outer casing wear more than the limit, light person knapper don't work well, don't rang rang, when heavy cylinder under scrap, so the inner sleeve than when wear limit must be replaced, in general normal use within a set of service life can reach 2000-3000 hours, but if started with 7 years, a lot of smart people began to use inferior materials to do the inner sleeve, prices vary a lot, of course, also sent a lot of quality, the same SB81 inner sleeve, inferior price about 200-300 yuan or so,Good quality is about 400-500 yuan, although the price is twice the difference, but the inferior service life is only 500-900 hours, quality and time limit and the human and material resources you are willing to choose which is the same?