Norton Square File Slip Stone 4" x 1/4". Square File applications range from dimensioning keyways to maintain fit, stoning faces on router bits, touching-up edges of reamer teeth, and lapping/honing to close tolerances to produce the finest edge on precision instruments, die work and delicate tools.To improve sharpening & reduce clogging, use with oil. Composed of an aluminum oxide abrasive. Oilstone made by Norton, Saint Gobain. Model FF14.