Norton Triangle File Slip Stone 4" x 3/8". Used for a variety of deburring, chamfering & radiusing applications including cleaning tap threads, stoning cutting surfaces of milling cutters, lapping honing tools, dies & molds, & putting precision points on center punches.To improve sharpening & reduce clogging, use with oil Composed of an aluminum oxide abrasive. Oilstone made by Norton, Saint Gobain. Model FF134.