1/4 Tap Drill Size

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As a DIYer, damaging the material you are drilling into can be embarrassing and frustrating. And to avoid spending too much on a project, you must first understand important details like the drill bits you need for a 1/4 tap drill size. 

Keep reading to discover the right tools for your job.

Drill Bit Sizes for a 1/4" Tap

A #7 drill bit with a diameter of 13/64″ (0.203″) is the best overall size for tap threads of 1/4″-20 UNC.

Tap Drill SizeDrill BitDrill Bit Size
1/4″ 20 #77/32″
1/4″ 28 #3#1
1/4″ 32Jul-32#1

How Does Sizing Work for a 1/4" Tap?

The thread pitch or number of threads per inch is the first part of the equation. You can thread one-inch drill bits with either 20, 28, or 32 threads per inch.

If you’re unsure about the thread pitch, it’s usually better to go with the lowest or “coarsest.” 

But fine threads or “fine” threads might be helpful if you need to ensure accurate adjustments or drill into tough materials. Even though they are more susceptible to tangling, they aren’t always the best option.

drill bit size for a 1/4

Harder materials, which require a tighter connection to the screw or bolt, would require a tap drill with a reduction of 50% instead of the standard 75%.

You need to use finer threading of 50% when tapping stronger materials. For a 50% tap drill, the recommended drill bit size for 1/4′′ 20 tap is 7/32″.

How to Calculate the Tap Drill Size for 1/4"

There are a variety of 1/4″ taps that require different drill bits. You can use any one of four different drill bits for 1/4″ taps, depending on the threads per inch and the size of the tap drill you’re using.

When selecting a drill bit for a 1/4″ tap, it’s crucial to consider the desired number of threads per inch and whether you’ll be drilling harder or softer materials.

When changing the thread count or moving between soft and materials, factors like overall breadth affect how much drill bit sizes change. It’s not quite a linear [1] development.

Because no two alterations are the same, there’s no way to predict the size to use based on a mathematical formula. Instead, use tap drill size charts like this to learn the drill bit sizes for each tap size, so you’re not relying on memory alone.

Why Do 20" And 28" Taps Require Different Sizing?

A #7 drill bit for a 1/4′′ 20 tap has a 75 percent thread, and a 7/32′′ bit has a 50 percent thread, respectively. 

For the 50 percent thread, we’ve seen other people recommend a 13/64′′ bit. It’s recommended to use a #3 drill bit for 75 percent thread or a #1 drill bit for 50 percent.

tapping hole

Because it is the industry standard, a 1/4″ 28 tap at 50% thread stands out from nearly every other thread size. One reason 1/4″ taps are so popular is that they’re easier to memorize than 7/16″ taps.

However, the coarsest threads are the most commonly used. Although the 28 tap is technically in the middle of the default range, the 20 tap is more commonly used in projects.


Now that you know what drill bit you’ll need for 1/4 tap drill size, all that’s left is putting your newfound knowledge into action. Drilling into new materials can be challenging, so it’s best to practice a few times before you get to business with your project.

To be a good driller, you’ll need to know all about the different drill bits and how they work. Drill bits aren’t all the same size, as you may be aware. A variety of sizes are available for a variety of uses.

Robert Johnson is a woodworker who takes joy in sharing his passion for creating to the rest of the world. His brainchild, Sawinery, allowed him to do so as well as connect with other craftsmen. He has since built an enviable workshop for himself and an equally impressive online accomplishment: an extensive resource site serving old timers and novices alike.
Robert Johnson
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