It can be annoying when you accidentally damage the material you’re working on. To save yourself from overspending and hassles, it’s crucial to know the right drill bits, especially for something like a 1/4 tap drill size.
So, in this post, let me guide you to the right tools for your project.
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 Size | Drill Bit | Drill Bit Size |
| 1/4″ 20 | #7 | 7/32″ |
| 1/4″ 28 | #3 | #1 |
| 1/4″ 32 | Jul-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.
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.
Other related articles:
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.
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.
Conclusion
Now that you know the right drill bit for a 1/4 tap drill size, give it a go! Drilling can be tricky, especially with new materials. So, maybe test it out a few times before diving into your main project.
You see, understanding drill bits is key. They come in all sorts of sizes, each designed for a specific job. Just something I thought you should know.
Robert Johnson is a passionate furniture maker & carpenter, sought after for his knowledge on the craft.
You’ve probably seen his down-to-earth wisdom in USA Today, Bobvila, Family Handyman, and The Spruce, where he has shared commentary and guidance on various woodworking topics.
Robert is the brain behind Sawinery, where he aims to share tips, tricks, and a passion for all things carpentry.
