Sharpstone grinders are made out of aircraft-grade aluminum and have specially designed diamond-shaped teeth to grind with ease. They use a poly O ring around the top, which makes grinding even easier because of the lack of friction and also protects against metal shavings. With two super strong neodymium magnets, it ensures a nice and tight closure. They are some of the best selling grinders available on the market because of their quality and price point.