Do not drill any material unless you have the right tools prepared. I’ve been there, and chances are, you’ve already damaged some materials and are now wondering which drill bit size is right for a 1/4″ 20 Tap. Well, you’re in the right place! Let’s dive in and figure this out.
Drill Bit Size for a 1/4" 20 Tap
A #7 drill bit with a diameter of 13/64″ (0.203′′) is the best choice for 1/4′′ 20 UNC tap threads.
|Drill Bit Size
|1/4″ 20 Tap
|1/4″ 28 Tap
Tapping threads is a fairly straightforward process.
Based on the material’s hardness you’re drilling into, you might actually need to deviate from the recommended tap drill size. Trust me, not all materials are created equal, so it’s always good to be flexible with your tool choices.
The standard tap drill is 75% for most materials, but if you need a tighter connection with the screw or bolt, you may use 50% of the standard tap drill.
Steel, stainless steel, and iron are examples of hard materials. Aluminum, plastic, brass, and other softer materials are available. If unsure, consult the manufacturer’s instructions to ensure you’re using the correct size tap drill.
50 percent finer threading is recommended for tapping harder materials. When using a 50 percent tap drill, the recommended drill bit size for 1/4′′ 20 tap is 7/32″.
Here are the drill sizes for 1/4′′ screws with different threads per inch:
Threads Per Inch
Drill Bit Size (75% Thread)
Drill Bit Size (50% Thread)
What to Consider When Drilling 1/4" 20 Tap
In my experience, threads per inch are a key consideration when selecting a drill bit size. Generally, the larger the tapped hole, the higher the threads per inch, resulting in finer threads. This detail can really impact the quality of your work.
Decide whether you’ll tap at 50% or 75% when drilling any type of material. If you can drill through a scrap piece first, you may get a better idea of how you should tap depending on the material’s hardness.
The most important thing to remember about drilling through metal is that any drill will work.
Because you should turn your bits slowly when drilling into metal, your drill’s maximum speed does not need to be extremely high. A high torque level can aid the passage of tougher materials, although speed is unimportant.
How to Drill
Once you’ve decided on the size of the drill bit to use, you can begin drilling. At least two clamps should be used when drilling into the metal to prevent the metal from spinning and potentially injuring you.
When drilling anything, but especially metal, make sure to wear safety eyewear. The material being removed might be highly sharp, causing a lot of damage to eyes that aren’t covered. Heavy work gloves are also a good option.
To begin drilling, you’ll need to mark the location. You can use masking or painters tape to help keep the step drill bit in place and leave a nice mark.
A step drill bit is a unique bit designed to start with a small hole and then expand into a larger one. When cutting into various types of metal manufacturing and some tougher woods, it’s critical to understand when and how to utilize a step drill bit.
When drilling, I often find that using a center punch with a hammer makes a big difference—it creates a small divot that helps keep the bit in place. And another pro tip: always use solid backing when you’re drilling into thin or flexible materials. It prevents the material from deforming, ensuring a cleaner result.
Ensure your drill is at a 90-degree angle to the material you’re working with. Taping and screwing in bolts can be difficult at any angle.
Use a drill press or a guide for your handheld drill if possible. Use cutting fluid and maintain your drill bits’ sharpness regularly, and avoid allowing the drill bit to become overheated.
How to Use 1/4" 20 Taps
The goal of tapping is to create a threaded hole for a screw to fit into. Always have the bolt prepped beforehand to ensure you are on the right track during the tapping process.
After drilling the initial hole, you’ll want to deburr the hole’s edge and eliminate any sharp edges.
Furthermore, a chamfer at this point will make tapping much easier. Chamfering is simple with specialized drill bits, although you can also use regular ones.
Make sure to clean out any chips, dust, or other debris accumulated in or around the hole.
A 90° tap guide is useful when setting up the tap . It’s easy to lean to the side when applying so much downward pressure to the hole and tool we’re working on, resulting in a crooked tap. Take your time and follow the instructions in the tutorial.
When it comes to tapping threads into a hole, I use a specific technique that involves moving forward a bit and then reversing direction.
This back-and-forth motion is crucial because it prevents your tap or drill bit from overheating or breaking, especially when you’re dealing with the high torque needed to penetrate metal.
The most typical pecking includes turning a full turn of the tap in and then a half-turn out. To be even more careful, you could go a full turn, withdraw the tap completely, clean up the hole, go in two turns, and repeat until the hole is thoroughly tapped.
This method takes a long time but results in the most consistent thread tapping.
The coarseness of the threads you’ll be tapping based on the hardness of the material you’ll be drilling will determine the size of drill bit for a 1/4′′ 20 tap. Make a decision ahead of time, and if possible, test with scrap material to ensure you have the right tools on hand.
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.