The V-Drill Guide is the easiest way to accurately drill perpendicular holes on both round objects and outside corners. It works just as well on flat surfaces. Simply align the marks on the side of the jig to the desired drilling location and clamp in place. The V-Drill Guide is heat treated for durability and accuracy for the life of the tool. Drill guide holes are sized for ANSI standard drill sizes from 1/8" through 3/8" in 1/64th increments. Overall length 5-1/2".