What Size Is a Number 7 Drill Bit?

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If you have recently bought a toolbox, you might observe that there are different sizes and numbers of drill bits present in it. You might wonder what size is a number 7 drill bit, as if you are not familiar with the dimensions, it can be risky to drill holes in the material.

What Size Is A Number 7 Drill Bit?

The size of the number 7 drill bit according to the ANSI system is 0.2010 inches. This drill bit is usually used to tap a ¼ tap, but it does not sit well with different thread pitches. It sits well with the thread pitch of 24 and if the expected thread percentage is 75%.

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Figuring Out The Drill Bit Size

Figuring out the drill bit size is necessary to create pilot holes that will help the fasteners connect the materials securely.

Man picking out a drill bit
  • The bit’s diameter is the primary indicator of the drill bit size that you will be used for creating the pilot holes.
  • The size can also be measured by drilling a pilot hole and measuring its diameter. 
  • Usually, the tool kits have the drill bits with standard sizes, but if you follow the ISO standards, the measurements are always done in mm, and the ANSI system usually has their measurements in inches.
  • It is observed that most of the commercially used drill bits have narrower diameters than mentioned, as the trajectory can shift and create a wider hole.

Working Of The Drill Bit Size

There are few rules that are involved in the working of the drill bit size.

  • Match the diameter of the bit and the shaft of the screw without any account to the protruding threads. It allows the threads to cut into the material, making them reliable fasteners.
  • A straight drill bit will create a U-shaped pilot hole. Thus it is essential to observe the nature of the drill bit and the materials you are working with.
  • In the case of a tapered bit, there will be a V-shaped pilot hole. A tapered pilot hopes to demand a drill bit with a wider diameter.

Here is the link to a video guide about matching the drill bits with the screws you are working with

Calculating The Drill Bit Size

Here is the mathematical way of calculating the drill bit size of the number 7 drill bit.

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You should be aware of basic mathematics and the dimensions for ¼ tap with a thread count of 20 per inch.

  • To get the right diameter, measure it manually or read the number written in the tap specifications.
  • Once the diameter is measured, you need to move forward by putting the values in a formula that is DH=DMB-.0.130 (% of thread desired/Ni)
  • For a number 7 drill bit, the percentage of thread desired is 75%. Now solve for the value of DH.
  • Your answer will be somewhat around 0.2010 inches.

Here is the link to an in-detail step by step guide to calculating the size of any drill bit. If you are not that well versed with the calculations, this guide will be quite helpful.

Why Different Drill Bit Sizes For ¼ Tap?

The table might mention that the number 7 drill bit size fits well for a ¼ tap. You might wonder why we advise different drill bit sizes for ¼ tap.

  • The ¼ tap has three different thread counts that are 20, 28, and 32. Therefore, there is no way that the number 7 drill bit will work for each of them.
  • The length of the drill bit changes according to the threads per inch of the tap size, as the length of the tap is influenced by this reading.
  • Lowering the threads per inch shorter is the drill bit size, even though the diameter of the drill bit might not change at all.
  • If the thread pitch is being ignored while making the calculations, you will never find the drill bit that fits with tapping size.
Man drilling a hole in a wooden furniture

Move Forward With Drilling

Since you are familiar with all the dimensions and fundamentals about the sizing of the number 7 drill bit, it is high time you move forward with drilling. Here are some precautions you might consider taking.

  • Ensure you are aware of the tap sizing and the threads per inch you are working with, as the number 7 drill will not work for all the sizes.
  • Once everything is squared up, do not forget to test it on scrap material to be sure.

Frequently Asked Questions

How Can I Sharpen My Drill Bit?

Sharpening a drill bit is a short process that starts with examining the dull bits. Next, move forward with wearing the don goggles and switching on the bench grinder. Now hold the bits against the wheel at a certain angle. Do not hold it for more than 5 seconds and continuously dip the bit into ice water to cool it down.

Is It Worth Buying A Drill Bit Sharpener?

Buying your sharpener is a value for money, as it will save the hard work and money you will use to buy new drill bits after a certain use. The continuous sharpening of the drill bits also makes them relatively safe to use.

Which Drill Bit Is The Hardest In Nature?

Tungsten Carbide is the hardest drill bit, and its edge is comparatively longer than the drill bits of other metals. Since it is quite brittle than the cobalt alloy, it is used on the tip steel drill bits.


Several drill bit sizes to work with; thus, it is pretty normal to feel overwhelmed and confused, especially when you are new to the whole process. It suggested not being hasty with the process, cherish it, and the results will make you feel proud. Experimenting can avoid accidents, so keeping scrap material around to test is a good idea.

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An expert at home repair, remodel, and DIY projects for nearly 40 years. His first experience came in completely restoring an antique home. Completely redone from the inside out, and restored to its original form, the home is a featured design by renowned Southern California Architect Cliff May, considered to be the father of the California Ranch Home. Now Dennis spends his time on fine woodworking projects and tool comparisons.