1/4-20 Tap Drill Size in MM

A 1/4-20 tap is one of the most common thread sizes used in metal and wood work. It means the screw has a one fourth inch width with twenty threads in one inch. To make a hole for this tap, the right drill size is very important. In millimeters, the correct drill size for a 1/4-20 tap is about 5.1 millimeters. This helps create clean threads that fit well.

We will talk about how to find the tap drill size for a special screw called 1/4-20, and we will convert it to millimeters (mm), which is a metric unit.

What is a 1/4-20 Tap?

A 1/4-20 tap is a tool that makes threads inside a hole so a bolt can screw in tightly. The 1/4 means the tap is one fourth inch wide. The 20 means it makes twenty threads in one inch. It is part of the Unified National Coarse system, which many people in the United States use. People use this tap for car repairs, furniture building, or making machines.

For example, someone fixing a car engine may use a 1/4-20 tap to hold a part in place. It is strong and works well for many types of work. Want to know why this tap is special? Keep reading.

Understanding Tap Drill Sizes

A tap drill size is the width of the hole that someone drills before using a tap. It is very important because the hole must match the tap for the threads to hold well. If the hole is too big then the threads will be weak. If the hole is too small then the tap will not fit or it might break. There is something called a tap and drill chart that helps find the correct size.

For example there is a beginner who wants to know what drill bit to use and the chart will show the right one. If someone wants strong threads then using the correct tap drill size is the key.

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1/4-20 Tap Drill Size in MM

For a 1/4-20 tap the best drill bit size is number 7 which measures 0.201 inches. In metric it is about 5.1 millimeters. This size gives around 75% thread grip which means the threads are strong and still easy to tap. Why 5.1 millimeters? It is the closest metric size to 0.201 inches.

For softer stuff like aluminum a 5.0 millimeter bit might also work but the threads will be a little weaker. Think of making a hole in a steel plate for a machine part. If someone uses a 5.0 millimeter bit then the 1/4-20 bolt will fit just right.

• 1/4-20 means: The “1/4” part refers to the size of the bolt (in inches), and “20” means there are 20 threads per inch on the bolt.
• Convert inches to millimeters: Since 1 inch = 25.4 millimeters, we convert the 1/4 inch diameter into millimeters. So, 1/4 inch = 6.35 mm.
• Tap Drill Size Formula: To calculate the tap drill size, we use this formula:
  • Tap Drill Size = Major Diameter – (1 / Threads per Inch).
  • For 1/4-20, it becomes: Tap Drill Size = 6.35 mm – (1 / 20).
  • That gives us 6.35 mm – 0.05 mm = 6.30 mm.
• Recommended Drill Size: The best drill size to use is 6.30 mm for a 1/4-20 thread.

Converting Tap Drill Size to MM

There are times when someone has a tap size in inches but the drill bits they have are in millimeters. This can be confusing. That is why it helps to know how to convert the size from inches to millimeters.

To start with a 1/4-20 tap the recommended drill bit size is number seven. This bit is 0.201 one inches wide. But what if someone only has metric drill bits? Then they need to turn inches into millimeters.

It is simple to do. Just remember that 1inch = 25.4 millimeters. So if the bit size is 0.201 inches then multiply that by 25.4. The answer is about 5.1 millimeters.

That is why people say five point one millimeters is the correct size in metric. It is not exact but it is very close. This size gives strong threads and is easy to tap.

For example imagine someone is using a metric drill set to make a hole for a 1/4-20 tap. If they pick the 5.1 millimeter bit then the tap will cut smooth threads and the bolt will fit well.

If the material is very soft like plastic or aluminum then they may try a 5.0 millimeter bit. This gives tighter threads but it may be harder to turn the tap.

So converting from inches to millimeters is not hard. It just takes a little math and the right numbers. Using the closest metric size helps people work better with the tools they already have.

Want a quick way to check sizes? A tap drill chart with both inch and metric sizes can help. It shows the right bit every time.

Making Process of 1/4-20 Tap Drill Size in MM

The process of making a 1/4-20 tap drill hole in millimeters is simple when someone follows the right steps. This size is common and used in many small and big projects.

Choose the Right Drill Bit

For a 1/4-20 tap the size in inches is 0.201. In millimeters it is about 5.1. So the person needs a five point one millimeter drill bit. This size works best and gives strong threads.

Understand the Meaning of 1/4-20

• 1/4 means the screw is 1/4 inch wide.
• 20 means there are 20 threads (or ridges) per inch.

Convert the Size from Inches to Millimeters

• Use this formula: 1 inch = 25.4 millimeters.
• So, 1/4 inch = 25.4 ÷ 4 = 6.35 millimeters.

Use the Tap Drill Formula

The formula to find the tap drill size is:

• Tap Drill Size = Major Diameter – (1 ÷ Threads per Inch).
• Major Diameter is 6.35 mm.
• Threads per Inch is 20.

Do the Math

• 1 ÷ 20 = 0.05 inches (or its millimeter equivalent).
• Subtract this from 6.35 mm to get the tap drill size in mm.

Find the Closest Drill Bit Size

• Check standard metric drill bit sizes to choose the closest match.
• Usually, a bit close to 5.2 mm works best for a 1/4-20 thread.

Types of Drill Bits for 1/4-20 Tap Drill Size

There are different types of drill bits people can use for a 1/4-20 tap size. Each type works better for certain jobs or materials. Knowing these types helps pick the best bit for strong and clean threads.

Standard Tap Drill Size:

• For a 1/4-20 screw, the standard drill size is 6.5 mm.
• This size works best because it gives the screw just the right amount of room to fit tightly into the hole.

For a Slightly Tighter Fit:

• If you need the hole to be a little tighter, you might use a 6 mm drill bit.
• This is a bit smaller, so the screw fits tightly and won’t move around easily.

For a Looser Fit:

• If you want a bit more space for the screw, you could use a 7 mm drill bit.
• This makes the hole slightly bigger, the screw fits, but it’s not as tight as the 6.5 mm hole.

Converting 1/4 Inch to Millimeters

• Inches and millimeters are both units used to measure length.
  • Inches are often used in the U.S., while millimeters are used in many other countries.
• To convert inches to millimeters, you need a special formula.
  • 1 inch = 25.4 millimeters.
• Now, let’s convert 1/4 inch to millimeters.
  • You need to divide 1 by 4 (because 1/4 is one part of a whole).
  • Then, multiply the result by 25.4 millimeters (because 1 inch = 25.4 mm).
• Here’s the math:
  • 1 ÷ 4 = 0.25 inches
  • 0.25 inches × 25.4 mm = 6.35 millimeters
  • 1/4 inch is equal to 6.35 millimeters.

Calculating the Tap Drill Size for 1/4-20 Thread

To make a hole for a 1/4-20 thread the drill size must be just right. It should not be too big or too small. That is why it helps to learn how to find the correct size using a simple formula.

1. Understand the Formula

• To find the right tap drill size, we use this formula:
• Tap Drill Size = Major Diameter – (1 / Threads Per Inch)

2. What’s the Major Diameter?

• For a 1/4-20 thread, the major diameter is 1/4 inch.
• 1/4 inch equals 6.35 millimeters (since 1 inch = 25.4 mm).

3. What’s the Threads Per Inch (TPI)?

• The number “20” in 1/4-20 means there are 20 threads per inch.

4. Plug the Numbers Into the Formula

• Subtract (1 divided by 20) from the major diameter:
• 6.35 mm – (1 ÷ 20)
• 6.35 mm – 0.05 mm = 6.30 mm

5. The Tap Drill Size

• The tap drill size you need is 6.30 mm.

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Importance of Using the Correct Tap Drill Size

• Better Thread Quality: Using the right drill size helps create smooth and strong threads. This means the parts will fit together perfectly!
• Avoids Breaking the Tap: If the hole is too small or too big, the tool (called a tap) used to make threads can break. Using the right size keeps your tap safe!
• Saves Time and Effort: When you use the correct drill size, you don’t have to redo the job. It makes the whole process faster and easier.
• Prevents Wobbly Joints: If the hole is too big or too small, the parts won’t fit right. The right tap drill size makes sure everything lines up neatly.
• Helps in Stronger Fittings: When the threads are made correctly, they help parts stay tight and strong, so they don’t loosen over time.
• Better Safety: If the drill size is wrong, it can cause problems in your work, leading to accidents or parts not working well. Correct sizing keeps you safe.

Benefits of 1/4-20 Tap Drill Size in MM

There are many reasons why people like to use the 1/4-20 tap size. It is strong easy to find and works well with many tools. Using the size in millimeters also helps people who use metric drill bits.

Drawbacks of the 1/4-20 Tap Drill Size in MM

Even though the 1/4-20 tap size is popular there are some small problems with it. It may not work well for very soft or very hard materials. Also finding the exact millimeter size like 5.1 can be hard in some tool sets.

FAQs about 1/4-20 Tap Drill Size in MM

There are many questions people ask about the 1/4-20 tap drill size in millimeters. These questions help clear doubts and make tapping easier. Below are some common questions with easy answers for beginners.

Conclusion

The 1/4-20 tap drill size and how to convert it to millimeters is important when you want to make sure your threads fit perfectly. We learned that the 1/4-20 size means a 1/4-inch diameter and 20 threads per inch. By converting the size into millimeters, we can use the right drill bit to make sure the threads are clean and strong. Using the correct tap drill size helps your project go smoothly, and the wrong size could cause problems like bad threads or breaking tools. Always double-check your measurements, and you’ll be able to complete your threading projects with ease.

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