What Size of Drill Bit Should Be Used For a 1/4″ 20 Tap?

drill bit size for a 1/4" 20 Tap

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Do not drill any material unless you have the right tools prepared. But chances are, you’ve damaged your materials already, so you’ve come to wonder what drill bit size is appropriate for a 1/4″ 20 Tap? Find out below!

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.

Screw SizeDrill BitDrill Bit Size
1/4″ 20 Tap#713/64″
1/4″ 28 Tap#37/32″

Tapping threads is a fairly straightforward process.

Depending on the hardness of the material being drilled, you may need to use a different tap drill size than recommended.

drill bit size for a 1/4

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:

Screw Size

Threads Per Inch

Drill Bit Size (75% Thread)

Drill Bit Size (50% Thread)

1/4“

20

#7

7/32

1/4“

28

#3

#1

1/4“

32

7/32

#1

What to Consider When Drilling 1/4" 20 Tap

According to our experts, threads per inch plays a role in determining what size drill bit to use. The larger the tapped hole, the higher the threads per inch and the finer the threads should be.

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.

drill bits

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.

drilling and tapping hole

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.

Using a center punch with a hammer also helps well by leaving a divot for the bit to rest in. Always use a solid backing when drilling into a thin or flexible material to avoid deforming it.

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 produce a threaded hole for a screw to access, so always have the bolt prepped to give you a clearer picture that you are on the right track.

drilling initial hole for tapping

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 [1]. 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.

Pecking

This is a technique for tapping threads into a hole. This procedure entails moving forward for a short distance and then reversing direction. It helps keep your tap or drill bit from overheating or shattering under the tremendous torque necessary to penetrate through 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.

Conclusion

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 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 and women. 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