Made of high quality carbon steel, with fine workmanship, it is accurate measurement, no rust and is durable. Turn the nut in middle of compass to adjust the diameter of circles. Please do not adjust the diameter bigger than the maximum ones, or the compass will be broken and cannot be repaired. Geometry tools, perfect for math classes, drafting, architectural drawings, engineering designs, both mechanical design and construction. Good for students, teachers, engineer, designers, artists, etc. Specification: Material: Carbon Steel Color: Silver 100mm: Overall Length: 105mm/4.13inch; Maximum Span: 110mm/4.33inch 125mm Overall Length: 130mm/5.12inch; Maximum Span: 165mm/6.5inch 150mm Overall Length: 150mm/5.91inch; Maximum Span: 175mm/6.89inch 200mm Overall Length: 205mm/8.07inch; Maximum Span: 275mm/10.83inch 250mm Overall Length: 260mm/10.24inch; Maximum Span: 375mm/14.76inch 300mm Overall Length: 305mm/12.01inch; Maximum Span: 415mm/16.34inch Package Includes: 1 Piece Pencil Compass Scriber Note: 1.Please allow a little difference between the real item and the pictures due to monitors difference. 2.Please allow some measurement errors.