HALF ROUND SMOOTH FILE 6"|Half Round Files can be used on any surface -- concave, convex or flat. They are rounded on one side, and flat on the opposite side. They are available in several styles, including bastard, smooth, and second cut. The backs of bastard and second cut files (over 6”) are double-cut. The backs of all 4” and 6” files (and all smooth) are single-cut.