... limit for the engraving area, can engraving whatever plane or bend surface, No noise, No smell, No dust ... same time in the circumstance of engraving black or white mark on the various of metals by many people ... It just takes only 3 seconds for each mark, this product engrave any metals (includes of nonmetal ... plating, but for groove plating, hanging plating, or roll plating, it suit for all noble metals ...