Made of stainless steel, it has anti-rust and anti- properties. It is , it not rust in dry environment, and it is easy to store. You can use it for a long time without changing it frequently,compact and light in weight, easy to carry. Use these gauges to determine the thickness of the material before working to save time and material, they can help you quickly and accurately correct and resolve any wrong thickness, simply like to use this tool, the quality is great, and the numbers are very easy to read, even if the tool is dirty, you can still read without problems, it's a profesional tool, heavy and feels great on the hand. Size: diameter 1.57 inch(4 cm); and small size, easy to use and carry. Designed for gaging steel music wire, has a range from wire gauge numbers 12 to 24. Suitable for piano tuning tool, measurer for piano music wire and chord. Colour:silver Material:Stainless steel Package Contents: 1 x Piano String Ruler Only the above package content, other products are not included. Note: Light reflection and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.