The small diameter (0.047”) reference bits allow you to drill a reference hole through material to check for obstructions, knots or other undesirables, and as a reference point to measure when drilling up through a top plate, or up from a basement through any kind of insulation. The hole created is so small it will remain unnoticed and does not need refinishing. Simply cut at an angle to create a point at the length you need and drill. When using, the drill chuck must be fully closed and tight.