The Crescent Nicholson half-round second cut files are ideal for materials containing iron, mild steel, plastics, and wood. The shape 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 second cut files allow you to quickly remove material from the work piece without leaving a very rough finish. Second cut, American pattern flat file. Perfect for use on concave, convex, and flat surfaces. Two-sided file is rounded on 1 side and flat on the other, so you can round out holes with ease. Two-sided file is rounded on 1 side and flat on the other, so you can round out holes with ease.