1/2-13 Tap Drill Size

If you buy something through our posts, we may get a small commission. Read more here.

Share It

Drilling can be a straightforward task. However, you can mess up everything if you don’t have the right drill size. Finding the correct 1/2-13 tap drill size for your project can help you finish your project faster and appropriately.

We have prepared some tables below and things to consider when choosing the right drill bit size.

What Size of Drill Bit Do I Need for a 1/2-Inch 13 Tap?

Our team crafted a tap drill size chart below to help you visualize which size of drill bit you should use for a 1/2-inch 13 tap. It shows the screw size, drill size, the equivalent fraction, and decimal in inches and millimeters.

Screw SizeDrill SizeClosest Fraction EquivalentDecimal (in)Decimal (mm)
1/2-13 NC27/64”27/64”0.42210.716
1/2-20 NF29/64”29/64”0.45311.509
1/2-24 NS29/64”29/64”0.45311.509

As you can see, the 1/2-13 tap requires a different drill size compared to the 20 and 24 taps. Knowing this can help you buy the right one that you need, saving you money and other resources.

1/2-13 tap drill size

Another table below shows the thread percentage you should use based on the material you will create a pilot hole into. This table shows the screw size, major and minor diameter, threads per inch (TPI), 50% thread, and 75% thread.

Screw Size

Major DiameterThreads Per Inch (TPI)Minor Diameter50% Thread (Steel, Stainless, & Iron)75% Thread (Aluminum, Brass, & Plastic)
Drill SizeDec. Eq.Drill SizeDec. Eq.

If you’re going to use harder materials, such as steel, iron, and stainless, a 50% thread is a better choice. It prevents chipping or creating an angled pilot hole into the metal. 

You can use a 75% thread if the material is softer and can be drilled easily, such as plastic, brass, and aluminum [1].

Considerations to Take Note of When Drilling a 1/2-13 Tap

Taking some things into consideration before drilling a 1/2-13 tap can also help you do the project properly. It also helps in preventing damage or accidents while working. 

First, identify the type of material you will work on. It will help you find the right drill bit size, thread percentage, and correct drill bit. To ensure that you have the right drill bit, try drilling onto a scrap piece of the same material. This also applies to other taps, like a 5/16” or ⅛” NPT.

Drilling Process and Steps

Now that you know what tap drill size to use, let’s go through the drilling process and steps. 

1. To avoid spinning, slipping, drilling out of place, or at a wrong angle, fix the material between clamps or drill it not so tightly on a scrap piece. Missing this step can end up in injury or drilling at the wrong spot and angle.

tap drilling with a clamp

2. Mark the spot where you want to drill. Wear safety gloves and goggles. Mark the area using painter’s tape to keep the drill bit in place and prevent leaving tape marks afterward.

3. Drill perpendicularly on the surface. A different angle will cause problems when you do the screwing or tapping of the bolts.

4. The drill bit should not overheat to prevent damage. Use cutting fluid and sharpen the drill bit for easier drilling.

5. If you are using a hand-held drill, use a guide or a drill press.

Using 1/2-13 Taps Properly

If you are done drilling the pilot hole, it is now time to use the 1/2″-13 tap. You’ll know if you have created the right drill hole or not. Here’s how to use the 13 taps properly.

1. After drilling, remove the sharp edges around the drill hole. 

2. Add chamfer using either normal or specialized drill bits to make the tapping easier.

tap hole

3. Clean the rest of the debris or dust around the hole.

4. Use a guide while applying pressure on the material and hole. Otherwise, you will have a crooked tap or a damaged hole. Slowly but surely, do the tapping to prevent damage and repeat the process from square one.


Pecking is one of the safest ways to insert the tap into the hole. If you have the correct tap drill size, you can do pecking to make your job safer. Pecking prevents the drill bit from overheating and damaging your tools and materials.

As a common practice, you have to rotate the handle in a full turn, and half turn back. Pull it out slowly and add oil on the surface and the tap before doing a full turn again.


Using the right 1/2-13 tap drill size can help you with your drilling project. It will help prevent damage and unnecessary spending of resources if you begin with the right tools. Don’t forget to check out the tables provided above as your guide.

Robert Johnson is a woodworker who takes joy in sharing his passion for creating to the rest of the world. His brainchild, Sawinery, allowed him to do so as well as connect with other craftsmen. He has since built an enviable workshop for himself and an equally impressive online accomplishment: an extensive resource site serving old timers and novices alike.
Robert Johnson
Related Articles
Join our community on facebook and get 3 woodworking plans for free!

Join Our Woodworking Community on Facebook And Get 3 Woodworking Plans for Free!