Rounded On One Side, Flat On The Other. Used On Concave And Convex As Well As Flat Surfaces. The Backs Of All Half Round Bastard Files Are Double Cut. The Backs Of All Half Round Second Cut Files Longer Than 6 Inches Are Double Cut, The 4 And 6 Inches Files Are Single Cut. The Backs Of All Half Round Smooth Files Are Single Cut. The Flat Sides Of All Half Files Are Double Cut.