10″ Half Round American Pattern Double Cut Bastard File (21858N) by Nicholson®. The Nicholson half-round double-cut bastard files are ideal for materials containing iron, mild steel, plastics, and wood. The coarse grade is perfect for use on concave, convex, and flat surfaces. The two-sided files are rounded on 1 side and flat on the other, so you can round out holes with ease. Half-round bastard files are double-cut on the rounded sides, allowing you to quickly remove material from the work piece.