BIG GATOR TOOLS STD2000DGNP V-DrillGuide is like a portable drill press for precision drill bit alignment! The precisely milled V-groove along the bottom of the drill guide allows for perpendicular alignment with all drill sizes on round parts like pipes, dowels and outside corners. Bottom surface is precision ground to assure stability and accurate perpendicular alignment on flat surfaces. The flat side allow 90° drilling into flat surfaces-just clamp and drill. Drill guide is sized for 9 Standard Imperial Fractions (SAE) drill bit sizes from 3/8, 25/64, 13/32, 27/64, 7/16, 29/64, 15/32, 31/64, ½". 9 SAE hole sizes to work with. Guides are made from special nickel alloyed steel that is heat treated for durability. Drill straight - every time! | BIG GATOR TOOLS STD1000DGNP V-DrillGuideTM is like a portable drill press for precision drill bit alignment! The precisely milled V-groove along the bottom of the drill guide allows for perpendicular alignment with all drill sizes on round parts like pipes, dowels, and outside corners. Bottom surface is precision ground to assure stability and accurate perpendicular alignment on flat surfaces. The flat side allow 90° drilling into flat surfaces-just clamp and drill. Drill guide is sized for Standard Imperial Fractions (SAE) drill bit sizes of 3/8" drill index-everything from 1/8" to 3/8" in 1/64" increments. 17 SAE hole sizes to work with. Guides are made from special nickel alloyed steel that is heat treated for durability.