PCBN inserts for turning cast iron and hardened steel: pcbn is the second hardest material in the world, and cbn related high precision cutting tools are introduced to industry, achieved high productivity and cost reductions. pcbn is the short name of polycrystalline cubic boron nitride, and pcbn inserts are mainly for the hard metal turning to replace the conventional machining way of grinding.. Choose from our selection of stainless steel thumb screws in a wide range of styles and sizes. In stock and ready to ship. "/>M8 43mm screw home depot