# Readers ask: What Size Drill Bit Do I Need For A 14 20 Tap?

To Tap This Size Screw Or Bolt: Use This Drill Bit: (Closest Fractional:)
12-32 NEF #13
14-20 NS #10
1/4-20 NC #7 13/64″
14-24 NS #7

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## What size hole do I drill for a 1/4 20 tap?

For a 1/4-20 bolt, the optimal drill bit size is #7 or 13/64th.

## How do I know what size drill to tap?

As a rule of thumb, for Metric threads, the tapping drill can be calculated by subtracting the pitch from the diameter of the thread. eg for an M5x0. 75 thread the tapping drill is 5-0.75mm = 4.25mm. For Imperial (inch) threads the tapping drill size is calculated in the same way, diameter minus pitch.

## Is 3/8 drill bit the same as 10mm?

3/8″ bits have a nominal size being just ever so slightly under 10mm. You can’t drill a hole of any size and put something in it the same size. It must be a bit smaller than the hole you drill.

## What is tap size?

A tap removes material from a pre-drilled or punched hole. The result of this cutting action produces threads within the drilled hole. Thread size is the number of Threads Per Inch (TPI) which is measured along the length of the tap. Metric sizes are referred to as thread pitch.

## When drilling a hole that has to be tapped the drill size should be?

A good tap drill is 85% (± 2 pp) of major diameter for coarse threads, and 90% (± 2 pp) of major diameter for fine threads.

## What size is a number 7 drill bit?

A number 7 drill bit is 0.2010 inches. As a fraction, the 0.2010 decimal is 201/1000.