The BIG GATOR TOOLS V-DrillGuide is like a portable drill press for precision alignment! V-groove along the bottom of the guide allows for perpendicular alignment with all drill sizes on round parts and corners. Bottom surface is precision ground to assure stability and accurate perpendicular alignment on flat surfaces. Metric Drill guide is sized for metric drill bit sizes of 3mm to 9.5mm in 0.5mm increments plus 3.3mm, 4.2mm and 6.8mm. Standard Drill guide is sized for fractional drill bit sizes of 1/8" to 3/8" in 1/64" increments. Guides are made from special nickel alloyed steel that is heat treated for durability. Drill straight - every time!