Atoplee 3V Edge Finder Electronic Optical Edge Finder with LED and Beep for CNC Lathe this will work on any metal object that is grounded. works like continuity tester. complete circuit Shank Diameter 20MM Probe Diameter 10MM Battery: 2 pcs ,AA,1.5V;model:N(high:28-29mm,diameter:11.5-11.9mm), (The battery is not include because of customs' policy Package Included: 1 x Electronic edge finder