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What Size Drill Bit Should Be Used for a 14-20 Tap?

A tap is used to cut a female thread to match the thread on bolts.
bolt image by martini from Fotolia.com

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.

Sizing

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.

 

Drill Size

A 14-20 tap requires a #10 drill bit. An ANSI #10 drill bit’s diameter is 0.1935 inches.

 

1/4-20 Tap

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.

 
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