What Size Drill Bit For 1/4 20 Tap (Briefed + Steps)

You might have seen woodworkers carrying varieties of tools to fix your home. Maybe you have tried tapping bolts but find yourself having difficulty, right? Each tap comes with different threads and bolts, etc.

We understand where you could have fallen behind. So, what size drill bit for 1/4 20 tap?

Licensed Electrician Bob Weiss says that a 1/4″ drill will not work at all, as it is the clearance hole size, and is too big to accept the threads for either. A 1/4″ bolt of either pitch will pass right through a 1/4″ hole.

The PROPER tap drill for a 1/4″-20 thread is a #7, which is 0.201″ diameter. For a 1/4″-28 thread, use a #3 drill (0.213″ diameter).

A 7/32″ drill is 0.219″ and will result in sloppy, weak threads on a 1/4″-20. A 13/64″ (0.203) drill would be a better choice if you only have fractional sizes available. 7/32″ is likely “close enough” for a 1/4″-28 unless we are talking about high-precision work.

Worry not, we bring this article for your in-depth questions. Carry this article if you want an overall picture! 

What Are The Differences Between Drilling And Tapping?

Starting discussions with some prerequisites for your benefit. The guideline to know the 1/4 20 tap drill size must cover these topics. Before knowing what size drill bit for 1/4 20 taps, get the differences first. 

Well, thinking what differences do these two actions hold? Interestingly, you are not alone! Let’s break all misconceptions down. 

With the help of a drill bit and motor, drilling creates smooth holes. Meanwhile, tapping comes with making a thread into the hole’s side.

You can also turn a treadmill motor into a power-tapping head.

The purpose behind making a tap has some motives. First of all, tapping builds a threaded hole so that bolts can get entered. 

Visualizing the bolt’s size into the head helps a lot while tapping. Now, let’s get familiar with the overall procedure to drill and tap!

Drill Bits With Reamers

Wondering why the header is containing reamers? Well, creating a hole for tapping is not just famous through drill bits. 

Reamers can also be added to proceed with tapping. Yes, you hear right! Reamers come along with drill bits if required. 

Reamer- a quite popular tool in the wood or metalworking world, it operates like rotary cutters. 

Along with that, reamers can suitably remove tinier amounts of materials. And this process happens before drilling the hole’s internal girth.

Maintaining your drill bit along with the reamer guarantees accurate measurements. However, some rules to be followed while using a reamer. 

Technicians usually drill a negligibly diminutive, primary hole. This measurement helps them gain a distinct interior diameter utilizing reamers.

How to Employ a 1/4″ 20 Tap

Once you have done initial hole drilling, it’s good to de-burr the hole’s edge. And try removing sharp edges if they exist. 

Here’s a bonus tip for you at this point: including a chamfer makes tapping much more effortless. 

More interestingly, chamfering requires no specialized drill bits. While using an ordinary bit, you may easily chamfer.

Also, try cleaning the chips or debris out. Accumulating these at the hole keeps further barriers away. So, never forget to do it!

Tapping threads into the hole has several manners. Pecking is one of them which includes a going-forward process. Later, it backs off within a short distance. 

As a result, the tap or drilling bit stays cooler. Due to overheating, various consequences are there to spoil your drilling. Can’t thank the pecking process enough! 

It brings special characteristics not to break the drill bit while applying excessive torque. 

Tapping like going in for a full turn comes with the highest benefits. Along with that, you can remove the tap. And then clean the hole up. Then again start tapping twice or more. 

It will ensure later a fully tapped hole to go through. That’s how pecking can build an evenly threaded tap.

What Size Drill Bit For 1/4 20 Tap

Let’s cut this specification into two parts. Then, 20 tap stands for threads number per inch. Meanwhile, 1/4 inches indicate the measurement of nominal diameter. 

However, each specific tap comes with a drill bit number. Several drill bit numbers are there to serve on the specific tapping.

Want to know the size drill bit for 1/4 tap? Well, #7 is the drill bit number here. And, 13/64 inches (0.203″ diameter) is the optimal 1/4 20 drill size. 

Let’s observe this table below which shows how randomly the numbers get changed:

Screw Size (inches) Threads Per Inch Bit Size

75% Thread

Bit Size

50% Thread

1/4 20 #7 7/32
1/4 28 #3 #1
1/4 32 7/32 #1

Got this table into the head? No worries, nothing is there to get remembered. All you need is to follow specific steps. Let’s explore!

Steps To Drill And Tap For 1/4″ 20 Bolts

Knowing the actual process stays as the topmost priority, right? Most users make mistakes on basic points. Our concern lies in letting you not do the same. 

Drill and tap- both are considered a major part of fabricating metal. Having a drill bit is a must-call for the robust tapped hole. Also, an ideal drill bit earns you producing a standard hole to fit your bolts in. 

Another misconception is- having a too-small drilled hole. Don’t dig it smaller! The bolt will end in damage. Also, it gets inconvenient to thread in. Meanwhile, digging a bigger hole results in a lack of structural strength. 

Step 1: Measuring

Measuring the location where you are tapping stays first. Make an approximate guess with a tape measurement. Then, put a mark there with the scribe.

Step 2: Marking

Now, mark the point of the center punch where the first tap will hit on! Bring a hammer and hit the back of this center point with it. 

This action will proceed to leave a divot to that hole. As a result, the drilling bit will be kept away from wandering. 

Step 3: Drill Insertion

Done with measuring! So does the marking! All we need is drill bit insertion into the drill. Ensure yourself that the chuck of the drill gets tightened. 

It protects the bit. Now, drop the cutting fluid down to the drilling bit. 

Step 4: Applying Pressure

Keep applying force to the drill so that it cuts the hole dipper. Don’t pressurize the bit once for a long time. Stop, and do it again. 

This gap between drilling must include cutting fluid. As a result, the metal piece and the drill bit will stay cool and be cutting-friendly.

Step 5: Turning On Handle

Insert this tap to secure into a tee handle now. See if it comes earlier or stays loose from the handle or not. 

Well, it indicates chances of tap breaking may occur while threading of the metal piece. So, quickly make the tap wet with fluids. 

It’s time to restart the tap in the hold again. But make sure to balance the handle level. Shift the handle clockwise to thread the 1/4-20 tap drill into the hole. 

Make an anti-clockwise turn of the handle if the tap binds. That’s it, continue this process to turn the tap. And keep running the tap through the hole actively. 

Do it until the tap bottoms out. Then remove the tap by turning the tap anti-clockwise.

Step 6: Completing Tap

Last but not least! Connect the flapper wheel to the grinder. You will burr in this grinder. Keep the burr away from each side of the hole.

Finally, bring a 1/4-20 bolt threading to the hole. It indicates whether the hole gets threaded nicely or not. If you face trouble threading the bolt, then start cleaning the tap. 

Then typically apply fluids into the hole and tap. That’s how you get drilling and tapping for the 1/4-20 bolts.

Some Other Contemplations For Drilling 1/4 20 Tapping

What we intervene above doesn’t cover the whole picture. So, it’s time to discuss the remaining parts so that you get this article complete:

  • While drilling any materials for tapping confronts you if you tap with 50% or 75%. So, make yourself sure of that. 
  • This rate may change according to the hardness of that material. So, try initially drilling through a scrap portion first. It will boost your confidence in making the final tap suitably.
  • After deciding which piece of material to drill, just start the drilling process onwards. First, always use safety goggles and thick gloves.
  • Get the piece to mount or put into any tightened condition. Using clamps is useful in this process. So, keep the piece stable by using two clamps.
  • For the long run, no metal spin or womble would happen. Your hands will get secured from any injuries.
  • Keep the drill to the material perpendicularly at 90 degrees. Users barely remember this small but vital point.
  • As a result, several bolt screwing or tapping issues may arise. Carry a drill guide or press for your own help.  
  • Keep honing your drill bits regularly. Also, ensure not to catch the warmness of the bit.


What Does A 1/4-20 Tap Indicate?

The thread size stands for the nominal diameter is 1/4″ for its 1/4 20 taps. 20 threads per inch mean the thread per inch will be 1/20= 0.05! Meanwhile, threads are created through a special pentagram machine. It carries the proper thread out with the help of a threaded rod. 

Is Drill Bit A Tool?

Drilling bit comes as a specialized wood-based tool. This drilling tool is also known as a twist drill. Drill bits are one of the most typical and multi-tasking parts of any appliance shop. Axis, body taper, drill diameter, point angle, shank, flutes, neck, etc., are the key terminology here. 

How Many Types of Taps Are Available?

Well, 3 types of taps you will find significantly. These are- bottoming tap, taper tap, and plug tap. You will find observable and prominent tapering of the cutting fringes in the taper tap. And, a plug tap is less prominent. 1-2 cut edges exist before having the full cutting force for the bottom.

What Does A 1/4 NPT Thread Mean?

The standard inner diameter of the fitting enlists NPT fittings. Usually, the outer diameter of threads comes with 1/4 inches. But it may differ in terms of your place. You need to measure the bottom outer diameter for male ends. For female ends, measuring across the top inner is required.

How Do I Size A Drill Bit?

Some ways are there to get the sizing. First of all, checking the shank is required. Then, tiny hand-held tools such as calipers are useful. Also, test holes are there letting you see if it fits. Besides, electric drills, screws, bolts, and flat metal pieces are required.


Get ideas of what size drill bit for 1/4 20 tap? Picking the correct number or size for your specific tap is a massive troubleshooter. 

We showed the differences remaining and how this 1/4 20 tap is suitably done. 

Still, get any confusion? Let us know in the comment section.

Jim Boslice

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