Compass Math Set, It is a zinc alloy 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 compass. You can accurately set the size of the circle you need and hold it The extension beam for drawing large circles, great for those need to big circle. Also includes a small pen that can be used in the slip handle or separately Everything packaged nicely in reusable clear case to protect and keep tools in one place, easy to carry and store Excellent for use in school or at home. The best circle drawing tool for engineers, draftsmen, teacher, student, artist, mathematician, carpenter etc. Specification: Material: Zinc Alloy Package Includes: 3 Pieces Graphic Compasses 1 Piece Extension Bar 1 Piece Drawing Pen 1 Piece Compass Refill 12 Pieces Refills 2 Pieces Replacement Pins Note: Color might be slightly different due to the color calibration of each individual monitor. Please allow slightly measuring deviation due to manual measurement.