Tap and Die Sizes Explained: The Basics

Tap and die Sizes Explained: The Basics

It’s crucial to cut threads and holes perfectly regardless of what type of repair you are doing. But figuring out the right diameter of the hole can be a bit tricky. That’s why today we’re presenting the ultimate tap and die sizes cheat sheet. We’ll inform you about the types of threads there are and why they are so important. Though we’ll primarily talk about tap sizes, the same principle works for the die as well. If you follow this comprehensive cheatsheet, cutting the threads or drilling the hole to the perfect size will become child play to you. So let’s get started, Shall we?

 

Why Are Tap And Die Sizes Important

As there are multiple measurement systems in action around the globe, it’s important to understand what size of tap and die you are using. If you are outside the USA, you can go fine by the metric system. But suppose you are used to following the USA standards. In that case, there are a couple of things you need to know about different sizes and measurement systems for taps and dies.

 

Thread Types

You may already know that there are mainly 2 measurement systems for tap and die. They are Metric and SAE (Society of Automotive Engineers). The SAE (Standard) system measures the external or internal threads of a tap/die (The thread pitch) by a unit named TPI (Threads per Inch). In contrast, the metric system showcases the distance between two threads in mm units. You’ll find plug taps, taper taps, and bottom taps in both systems.

Depending on the task you’ll need to do, there are a variety of thread types available. Let’s have a look at some most commonly used thread types across the globe. Shall we?

 

Matric

This is one of the first internationally agreed on general-purpose thread types that can be used all over the planet. This system provides V-shaped threads with a 60° flank angle. They provide two different types of pitch: coarse pitch and fine pitch. A Coarse thread is identified by diameter only, whereas a fine thread is recognized by diameter and pitch size.

 

NPT

The NPT standard is issued by American National Standards Institute (ANSI). The threads that abide by this standard have to provide a sealing agent like lubricant or tape so that no fluid gets leaked out. They offer tapered thread.

NPTF

They are almost similar to the NPT standard with distinction over the flatness of the peaks and valleys of the threads. It’s also known as “Dry Seal” Pipe Threading.

 

NPSC

NPSC Stands for National Pipe Straight Coupling. It is also known as “IPS Threads” or “Iron Straight Threads.” Straight pipe threads do not offer any sealing function.

NPSM

National Pipe Straight Mechanical (NPSM) offers a straight thread instead of a tapered one and requires sealants to make the connection leakproof.

 

NPSF

This is the Dryseal USA (American) Standard Fuel Internal Straight Pipe Thread. This type of thread ensures pressure-tight joints without the use of a lubricant or sealer.

 

NPSI

This is for internal use only. It is commonly known as Dryseal USA (American) Standard Intermediate Internal Straight Pipe Thread. It is a bit larger than the NPSF.

 

BSPT

BSPT (British Standard Pipe Taper) is similar to NPT, with a slight difference in the angle across the flanks of threads and the number of thread pitches. These types of threads provide parallel threading.

 

BSPP

BSPP stands for British Standard Parallel Pipe. It is most popular in the UK, Europe, Asia, Australia, New Zealand, and South Africa. This parallel thread fitting uses a bonded seal ring to do the sealing. These types of threads provide conical threading.

 

Let’s See Some Charts

Now, let’s have a look at how you can find the right tap and die sizes for your project:

 

Cheat Sheet For Standard Tap And Drill

Here is the cheat sheet to determine the perfect tap and drill sizes using the standard system (inch):

The Equation is:

Drilled hole size = Nominal outside diameter – (Double thread depth  x  Percentage of full thread)

Now let’s go through the chart below to find out the drilled hole size for the tap you’re using.

Threads Per Inch Double Thread Depth 50% Thread 55% Thread 60% Thread 65% Thread (Recommended) 70% Thread (Recommended) 75% Thread (Recommended) 80% Thread 85% Thread
6 .21651 .1083 .1192 .1300 .1408 .1517 .1625 .1733 .1842
7 .18558 .0929 .1021 .1114 .1207 .1300 .1393 .1486 .1579
8 .16238 .0813 .0894 .0975 .1056 .1138 .1219 .1300 .1381
9 .14434 .0722 .0794 .0866 .0939 .1011 .1083 .1156 .1228
10 .12990 .0649 .0714 .0779 .0844 .0909 .0974 .1039 .1105
11 .11809 .0590 .0649 .0708 .0767 .0826 .0885 .0944 .1005
12 .10825 .0541 .0595 .0649 .0702 .0755 .0808 .0861 .0921
13 .09992 .0499 .0549 .0599 .0649 .0699 .0749 .0799 .0850
14 .09278 .0464 .0510 .0556 .0602 .0648 .0694 .0740 .0789
16 .08119 .0406 .0446 .0486 .0526 .0566 .0606 .0646 .0691
18 .07217 .0361 .0396 .0431 .0466 .0501 .0536 .0571 .0614
20 .06495 .0325 .0357 .0389 .0421 .0453 .0485 .0517 .0553
24 .05412 .0270 .0298 .0326 .0354 .0382 .0410 .0438 .0460
27 .04811 .0240 .0264 .0288 .0312 .0336 .0360 .0384 .0409
28 .04639 .0232 .0254 .0276 .0298 .0324 .0347 .0370 .0395
30 .04330 .0216 .0238 .0260 .0282 .0304 .0326 .0348 .0368
32 .04059 .0203 .0223 .0243 .0263 .0283 .0303 .0323 .0345
36 .03608 .0180 .0198 .0216 .0234 .0252 .0270 .0288 .0307
40 .03247 .0162 .0178 .0194 .0210 .0226 .0242 .0258 .0276
44 .02952 .0147 .0162 .0177 .0192 .0207 .0222 .0237 .0251
48 .02706 .0135 .0148 .0161 .0174 .0187 .0200 .0213 .0230
56 .02319 .0116 .0127 .0138 .0149 .0160 .0171 .0182 .0197
64 .02029 .0101 .0111 .0121 .0131 .0141 .0151 .0161 .0173
72 .01804 .0090 .0099 .0107 .0115 .0123 .0131 .0139 .0153
80 .01623 .0081 .0089 .0097 .0105 .0113 .0121 .0129 .0138

Now, Let’s check out how to use this chart. It’s simple. Suppose you need to measure the hole size for 80% thread in a ¼ inch -20 TPI tapped hole. To do this, go down the first column and find the proper pitch count. In our case, that’s 20. Then, check for the corresponding percentage (80%). This gives us the value .0517. Lastly, subtract the value we’ve got from the outer diameter (0.250). So the diameter for our desired hole will be: 0.250 – 0.0517 = 0.1983 inches.

Pro Tip: Don’t forget to check if the pitch is too coarse for the diameter. The minimum diameter possible for the chosen pitch (x) is:

X = Double Thread Depth * 3

And another thing, We recommend thread percentages 65%, 70%, and 75%. This will give you the best results.

 

Cheat Sheet For Metric Tap And Drill

Here is the cheat sheet to determine the perfect tap and drill sizes using the metric system (inch):

The Equation is:

Drilled hole size = Nominal outer diameter – (Double thread depth  x  Percentage of full thread)

Now go through the chart below to find out the drilled hole size for the tap you’re using.

mm Pitch Double Thread Depth 50% Thread 55% Thread 60% Thread 65% Thread (Recommended) 70% Thread (Recommended) 75% Thread 80% Thread 85% Thread
4.0 5.1963 2.5982 2.8580 3.1178 3.3776 3.6374 3.8972 4.1570 4.4169
3.50 4.5466 2.2733 2.5006 2.7280 2.9553 3.1826 3.4100 3.6373 3.8646
3.00 3.8969 1.9485 2.1433 2.3381 2.5330 2.7278 2.9227 3.1175 3.3124
2.50 3.2476 1.6238 1.7862 1.9486 2.1109 2.2733 2.4357 2.5981 2.7605
2.00 2.5979 1.2990 1.4288 1.5587 1.6886 1.8185 1.9484 2.0783 2.2082
1.75 2.2733 1.1367 1.2503 1.3640 1.4776 1.5913 1.7050 1.8186 1.9323
1.50 1.9487 .9744 1.0718 1.1692 1.2667 1.3641 1.4615 1.5590 1.6564
1.25 1.6236 .8118 .8930 .9742 1.0553 1.1365 1.2177 1.2989 1.3801
1.00 1.2990 .6495 .7145 .7794 .8444 .9093 .9743 1.0392 1.1042
.90 1.1687 .5844 .6428 .7012 .7597 .8181 .8765 .9350 .9934
.80 1.0394 .5197 .5717 .6236 .6756 .7276 .7796 .8315 .8835
.75 .9743 .4871 .5359 .5846 .6333 .6820 .7307 .7794 .8282
.70 .9093 .4547 .5001 .5456 .5910 .6365 .6820 .7274 .7729
.60 .7793 .3897 .4286 .4676 .5065 .5455 .5845 .6234 .6624
.50 .6421 .3211 .3532 .3853 .4174 .4495 .4816 .2137 .5458
.45 .5847 .2924 .3216 .3508 .3801 .4093 .4385 .4678 .4970
.40 .5197 .2599 .2858 .3118 .3378 .3638 .3898 .4158 .4417
.35 .4547 .2274 .2501 .2728 .2956 .3183 .3410 .3638 .3865
.30 .3896 .1948 .2143 .2338 .2532 .2727 .2922 .3117 .3312
.25 .3246 .1663 .1785 .1948 .2110 .2272 .2434 .2597 .2759

Now, Using the same method mentioned above, let’s calculate. Suppose you need to measure the hole size for 70% of thread in an (M4) 4 mm x 1.00 tapped hole. To do this, we have to look for 1.00 threads in the first column in the table. Once we have found the thread, we look for the corresponding percentage (70%) and get a value of .9093.

Now subtract the value we’ve got from the 4mm diameter. So the diameter for our desired hole will be:

4 – 0.8444 = 3.0907mm

Pro Tip: We recommend thread percentages of 65% and 70%. This will give you the best results.

Don’t forget to check if the pitch is too coarse for the diameter. The minimum diameter possible for that TPI:

X = Double Thread Depth * 3

 

Final Words

That’s all for today. I hope this article proves to be helpful to those in need. Please feel free to share your thoughts and experiences with us in the comment section below. Use the cheat sheet to get that perfectly sized hole every time. Thanks for reading this far. Have a great day.