A tap is a metal-working tool used to cut threads for bolts and screws. A tap cuts threads into the sides of a smooth hole bored with a drill bit of a specific size relative to the size of the bolt or screw to be used.
Taps and Dies
A die cuts the male thread on a bolt or screw. A tap cuts the female thread into which the bolt or screw is turned to tighten pieces together. The female thread can be on the inner surface of a nut or a fixed metal object.
Machine screw sizes are described by two numbers. The first is a size designation, the second is pitch (threads per inch). A 14-20 tap cuts threads for a size 14 screw with a pitch of 20.
A 14-20 tap requires a #10 drill bit. An ANSI #10 drill bit’s diameter is 0.1935 inches.
A 1/4-20 tap is a different, slightly larger size than a 14-20 and should not be confused with it. This size requires an ANSI #7 drill bit, whose diameter is 0.2010 inches.