A deflection wedge is a wedge that when used properly is lodged into a hole that has just been bored. It directs the drill bit in further so as to create a proper hole.
The deflection wedge is used in precision drilling projects, such as installing molding onto the sides of a bookcase, or screwing something into the floor. The reason that the deflection wedge is used in these scenarios is that it causes clean drilling and won't go in crooked or leave a sharp edge behind.
Drilling holes into commonly seen areas of the house, as in the front of a piece of furniture or the wall, can cause ugly drill marks. Using a deflection wedge can prevent the hole from leaving frayed edges that sometimes come with repeated drilling to get the screw in straight. The deflection wedge can make the hole as unnoticeable as possible, and because it leaves behind a clean surface, you do not have to worry about sharp edges.
When using a deflection wedge, the best possible drilling match is a deflection bit. This cone-like bit works with the deflection wedge to drill into a borehole. The bit is long and therefore is perfect for fitting past the wedge and into the borehole.