Norton Diamond Shape File Stone 4" x 9/16" x 3/16". These diamond shaped stones are great for precision sharpening for cleaning acute angles in tools, dies & molds, & for stoning geometric chasers & sewing machine feeds.To improve sharpening & reduce clogging, use with oil Composed of an aluminum oxide abrasive. Oilstone made by Norton, Saint Gobain. Model FT134.