What Size Drill Bit For 5/16 Tap (Calculations)

Cutting threads seems easier than actually doing the process. Got yourself into drill bit picking issues? You are not alone! 

As several sizes for each specific tap are available, getting under confusion is quite normal.

So, what size drill bit for 5/16 tap do you require?

Before knowing the size of the drill bit for the 5/16 tap, understand its variety of taps.

The recommended drill bit size for a 5/16 tap is 17/64 inch. This provides a suitable hole size for tapping to ensure proper threading.

We will explore all of these here! So, let’s get going!

How Does Tap Sizing Suit To 5/16 Inches Tap?

WoodBeaver drill bits

As tap sizing relies on different variables, let’s find those variables first. The diameter of the tapping is the fundamental requirement for sizing. 

Also, the expected full thread percentage along with thread pitches decide your tap sizing. Meanwhile, drilled hole size recommends what drill bit you may require. 

Basically, a 5/16 inches tap comes in two different sizes- 18 and 24 inches. Users often think this variety shows different diameter measurements. 

But no! It only changes the thread pitch but the diameter. Also, it affects the 5/16 tap drill size.

However, let’s assume that you use a 5/16 inches tap or 8-32 tap! But the full thread percentage will not get affected through these. 

So, the only motive is to have an expected outcome. Relevantly, the full thread percentage range stays 70 to 85 on the basis of different tapping. 

However, there are some tapping formulas available. Using a hand, a mil, or even a lathe are the basic options to pick over. 

Calculation of Tap Drill Size For 5/16 Inches Tap

The size tap you are using is the base to find the tap drill size out. Our target is to know what size drill bit for 5/16 tap. So, let’s get the calculation done!

Requiring the diameter is the topmost priority. Wondering how you should measure? 

Well, it’s quite easier to measure physically. Also, you can go for the alternative. Just check the specification list of the tap. And that’s all.

Earlier we have known two different sizes a 5/16″ tap gets. However, for both- 18 and 24, it results in 0.3125 inches diameter. 

Now, It’s time to get into the formula:

DH or drilled hole size (in inches)= diameter measurement – 0.0130*(% of expected full thread/Ni).

Meanwhile, we found a diameter size earlier which is 0.3125, right? However, the full thread percentage relies on your expected thread size. 

For this example, we are using 75 whereas 70 to 85 is a good range. On the other hand, Ni appears as the number of threads per inch. If we consider 5/16″ with 18 inches tap, then Ni equals 18.

Finally, our hands reach all the variables for calculation.

After inserting all these, formula stands:

DH or drilled hole size (in inches)= 0.3125 – 0.0130*(75/18). 

The value comes to 0.2583 approximately. That’s it! Round the value so that you pick the nearest drill size for 5/16 tap

As per our 18-inch tap, 17/64 is the nearest drill bit size. Technicians consider it a fractional drill bit. 

Why Do 18″ And 24″ Taps Demand Different Drill Bit Sizes?

Why do different sizes of drill bit 5/16 tap we require?

Lucky that you are getting a chance to clear this misconception. Most users can not differentiate whether they need different sizes. 

As a result, drilling wood or metal gets imperfect or bolts find hole barriers. We get you covered. Even if these two taps contain the same diameter, which factor impacts the most? 

Simply, it’s the thread number per inch that keeps generating variation. This number affects the tap’s length. 

Generally, producing the same number of threads can not be done through different threads per inch. 18 taps are unable to produce as many as 24 taps, is it? 

The difference in length between these two taps demands variety at bit sizes. As the thread pitch carries an important part in the calculation, you can’t avoid this direct influence.

What Drill Bit Size To Use For A 5/16″ Tap?

As two types of 5/16″ tap are available, you will get two size drill bits. So, let’s not get it complicated. 

If you carry a 5/16″- 18 tap, a fractional drilling bit will be required. On the other hand, ‘I’ drill bit comes for a 5/16″- 24 tap. 

Both stand as per the drilled hole measurement. And the calculation we did to match with the nearest drilling bit size. Let’s get the overall picture of 5/16″ tapping below:

Screw Size (inches) Drill Bit Type Drill Bit Size (inches)
5/16″ 18 F 17/64″
5/16″ 24 I 17/64″

Types of Drill Bits

Already you got to know what drill bit for a 5/16 tap, don’t you? However, this article consists of drill bits, so do its characteristics. 

Several types it offers have distinct definitions too, right? Let’s spill the beans so that varieties of drill bits find you comfortable. Shall we?

Twist Drill Bit

For home or culinary usages, this drill bit has the maximum demands. This common type serves for generic purposes in wood drilling. 

Also, you may find it comfortable for plastics and lightweight metals.

Check a twist drill bit out below:

DEWALT DWA1181 21-Piece Set Check Price!
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Bosch TI14 Titanium Metal Drill Bit Check Price!

Auger Drill Bit

This wood boring drill bit comes with a screw tip. As a result, starting holes is easier. Relevantly, pulling this bit throughout the hole immediately cleans the area. 

The length, 18 inches or more, makes the large flutes removing dust or debris. The more chip, dust removal, the better. Auger bits carry far better effectiveness in removing these. 

It holds a hollow center for accelerating this process along with far boring down. However, drill bits get more robust via a solid center.

Brad-point Drill Bit

For boring wood or metal pieces, brad-point drill bits are famous. Its central bit tip helps in the positioning of bits. 

As a result, you can see during the drilling process. It also creates a cleaner exit point on that piece. Flutes start removing dust and chip to an extra-wide nature.

Self-Feeding Drill Bit

It also bores through the wood. A screw at its tip shifts the position correctly. However, this tiny and short bit does not carry standard flutes. 

So, yes! A bit more work is mandatory from your side. Pulling this bit backward period-wise is the main in this mandatory-working list. 

However, a cleaner hole by removing chips and dust is possible through it.

Installer Drill Bit

Considered as a special type of twist bit, it is used on security systems largely. More than 18 inches in length, it passes wood very comfortably. 

As it’s also known for installing wiring, you need wires to pass through holes. 

Spade Drill Bits

Also known as paddle bit, it shows boring diameter holes. Meanwhile, diameter’s range can be within 1 to 1.2 inches. 

The flat-shaped blades having a sharper point allow this bit to fix positions. Resulting in more neat and clean holes is a significant characteristic of spade bits.

Want to keep the cutting blade steady? The arbor keeps a pilot bit to do that.

Hole Saw

Yes, you see right? We have brought here a hole saw which is also a drilling bit. It enables cutting holes containing a larger diameter. 

Characteristics that keep it separated from other bits contain arbor and mandrel. Meanwhile, the mandrel works as a shaft including a shank. 

Additional Drill Bit Choices

The drill saw bits trim uneven holes and outline in wood and metal pieces. Meanwhile, pocket hole bits come with pocket jigs. 

As a result, you can drill holes containing difficult angles. Also, it allows screwing to build wood joints. Moreover, extensions of drill bits help to reach a long distance while drilling. 

How To Size Drilled Holes For Bolts?

Drill bits are intensely related to bolts and drilled holes. Let’s put the focus on these now! 

Your effort behind picking the suitable drill bit will go in vain without measuring holes. The imperfect size of bolt holes results in a loose connection. However, bolts or holes may get damaged due to over-tightening. 

So, maintaining a perfect connection is so crucial. To avoid all sorts of risky situations, following some steps is a must. 

There are basically two types of bolt holes- tapped and passing-through! Meanwhile, both of them show a unique clearance which builds strong connectivity:

Step 1: Gliding Bolts

Glide the bolt into a foreword of the bolt and thread meter. Then start shifting the bolt unless you find it sliding into the meter. 

The moment the threads sit replete with the gauge’s top edge is very crucial. Look at the bolt at the same time! If it stays stagnated, then all is good for your process.

Step 2: Pressurizing Threads

Now, shift the bolt to the thread area of the gauge. Now, apply force to the threads so that it goes against the gauge too. 

Until the threads fit evenly with the gauge, keep pressurizing! 

Once it is done, put down the accurate threads per inch. For example, a 5/16″ diameter bolt with 18 threads per inch is specified as a 5/16-18 bolt.

Step 3: Examining Combinations

You can choose drill bits containing 1/32″ which is more extensive than the bolt’s diameter. It will let the connection between a bolt and hole tighter. 

On the other hand, you may witness a loose connection too. For example, picking 1/16″ bit larger than the diameter of the bolt.

That’s the overall process to drill holes in! 


What Is The Method For Calculating Tap Drill Size?

This calculation must include the pitch and thread’s diameter of the drill. As a rule of thumb, find out the diameter of the thread first. Then, subtract the pitch from it. That’s how the tap drill size appears. For example, the drill size of an M5x0.75 thread will be 5-0.75 mm or 4.25 mm.

What Are The Distinguishable Sizes of Drill Bits?

Usually, bit size shows how lengthy the diameter of a body is. Its particular range goes from 1/16 inches to even 1/4 inches. However, there are other larger bits available too. You can have 5/16, 3/8, 7/16, 0.5-inch bits, and so on. Also, you may find different sizes in a specific tapping.

What Is The Difference Between Drilling And Tapping?

Drilling and tapping are two separate activities. Drilling directs to forming a smoother threaded hole. A drill bit contains thread count, pitch, diameter, etc. For this process, drill bits are highly operated. Meanwhile, assembling a thread into the side of that hole is the main job of tapping.

What Specialities A Brad-Point Drill Bit Holds?

Brad-point drill bits are developed in order to bore into wood. You will find this bit at the bit tip’s center. This characteristic helps users to have a more accurate drilling experience. Also, delivering a clean exit point is its superiority. It serves an extra-wide area to release more material.

What Are The Key Advantages of Drilling?

There are several drill bits you may find where the main motive stays the same. It is easier to set up or install and requires less labor. Maintenance cost is incredibly low. Gathering all required tools is largely available. Also, monitoring is quite simple.

Final Words

Reading this article still? Great, you already got what size drill bit for 5/16 tap, don’t you? 

We tried to distinguish the sizes between drilled holes, and drill bits. Keep following these details before having a 5/16″ tap. 

Hopefully, we could find you comfortable with woodworking.

Best wishes!

Jim Boslice

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