for Compass Math Set, It is a zinc alloy for compass. equipped with an adjusting wheel and an extension beam with an automatic locking mechanism, allowing you to accurately set and hold the desired circle size.With universal adapter and extension beam For math, geometry, art, drafting and drawing.By turning the middle of the screw to adjust the opening and closing for compass. You can accurately set the size of the circle you need and hold itThe extension beam for drawing large circles, great for those need to big circle. Also includes a small pen that can be used in the for slip handle or separatelyEverything packaged nicely in reusable clear case to protect and keep tools in one place, easy to carry and storeExcellent for use in school or at home. The best circle drawing tool for engineers, draftsmen, teacher, student, artist, mathematician, carpenter etc.Specification:Material: Zinc AlloyPackage Includes:3 Pieces Graphic Compasses1 Piece Extension Bar1 Piece Drawing Pen1 Piece for Compass Refill12 Pieces Refills2 Pieces Replacement for PinsNote:Color might be slightly different due to the color for calibration of each individual monitor.Please allow slightly measuring deviation due to manual measurement.