You are at a hardware store, looking for materials you need for a home improvement project. You quickly scan through your checklist and see drill bit and tap. Unlike screws or nails, which you can find almost everywhere, these materials may be new to you.

This article will provide a walkthrough of what you need to know as you work with drill bit and tap. The Frequently Asked Questions (FAQ) section at the end of the article should help you locate information quickly. 

A tap drill is a tool we use to cut an opening in a piece of metal. It has a cylindrical shape and comes in various forms and sizes. Cutting the threads inside a surface is called tapping. It’s typically done in metal. Tap drills come in several sizes to address a variety of applications. Thick ones would make a huge hole. It is useful in items that need a lot of support, such as attaching table legs to the main table. 

To calculate the tapping size in metric threads, subtract the pitch from the thread diameter. For example, if the thread size is M5 x 0.50, the tapping drill is 5 – 0.5 = 4.5 mm.

We use the same formula when calculating the tapping drill size in imperial threads. For example, if the thread size is 3/4.10 UNC pitch = 0.1 and the thread diameter = 0.75, the tapping drill size would be 0.65 or 16.5 mm.

Drill sizes come in different systems of measurement. The majority of the world’s population uses the metric system in measuring, so it only makes sense to talk about it. You express metric sizes in millimeters (mm). Sizes can go as short as 0.0483 mm or as long as 36.50 mm. The length to pick will depend on your needs.

The table below shows the tap drill size for the given thread size. If you cannot find your drill bit size, use the formula Thread Diameter – Pitch = Tapping Drill Size.

You may refer to the table below for a quick guide. 

When woodworkers are drilling a hole in a wood piece, the first hole they will drill is likely bigger than the screw size. If you have ever wondered, we call this the clearance hole. It is necessary for all woodworking projects. So, why do you need a clearance hole?

A clearance hole is smaller than the screw’s head but is a tad larger than the thread’s outside diameter. It results in a tighter joint between these pieces of wood. It also drastically reduces the risk of jacking, which is typically common in woodworking. Other materials aside from wood also require a clearance hole to prevent any materials from splitting or cracking. It does not look aesthetic and may weaken the hold.

Now you know why you need one. The next question is, how does it work? People won’t go the extra mile of drilling a larger hole for nothing. When screwing or joining wood together, the first step is to make a hole on the top piece of wood. It should be larger than the screw thread’s diameter. This hole would prevent the screw from attaching to the top piece of wood as you screw them together.

What happens if you do not have a clearance hole? The screw threads will bind against the grain of the top wood piece, causing it to separate. When this happens, the screw will tighten itself on the wood’s top portion but not pull the two pieces together. It would result in a few problems, such as a weak bond between pieces of wood.

The next question you might be asking yourself is, how deep does one need to drill it? Do you do it halfway, a quarter, or all the way? In most cases, it should be until the top material only. If you accidentally drill on both wood pieces, your screw will fall off. It defeats the purpose of having a hole.

When should you have a clearance hole? If you have a fully threaded screw, then you need it. Otherwise, don’t bother having one. What is the purpose? It prevents the bottom material from getting jacked by the top one. You want to avoid jacking as it could lead to issues in the long run. Partially threaded screws sometimes need a clearance hole. If the threads are at the top part, you will need it. Else, you won’t need it. A clearance hole is also a necessity when bolting wood together. But instead of using a screw, you are using a bolt. The hole should be slightly larger than the bolt shank.

Yes, a drill bit is needed when creating one. Some people would make a hole using the screw itself by screwing into the top portion of the wood piece, then unscrewing it out. The idea here is to create a hole using the screw.

Do not use a screw to create a clearance hole. The screw will only create an equally big hole. The threads will also bind with the wood, causing it to be ineffective. Driving a screw directly into the piece of wood will create cracks. Over time, these will grow bigger. It results in a loose fit.

The bottom line, take time and save some money to get yourself a drill bit. Use it to drive a hole correctly and safely. A good quality tool from a reputable brand should last you a few years.

Aside from preventing jacking, here are the other benefits of having one:

When it comes to size, there is no size fits all. It would depend on the type of material you are working with, but it would have to be a little bit larger than the thread’s outside diameter. In measurement, that is about 1 mm.

If you are working with softwood, the clearance hole should be similar to the size of the screw’s thread. On the other hand, hardwood would need a larger hole. It helps the head to flush out with the wood’s top piece. It may not apply to all scenarios but is generally correct.

Several size charts are available online, but these could lead to confusion. A useful tip is to create a hole that is 1mm larger than the diameter of the thread. Keep in mind to only have the hole through the wood’s top piece. 

A clearance hole should not interfere with the screw threads regardless of the fit. Again, this hole is there to give way for the screw to reach the second piece of wood. Now, how are these fits different from each other? In terms of allowance, they differ. In terms of functionality, they all serve the same purpose.

A normal fit does not provide less support than a close fit. Similarly, a free fit does not provide less support than a normal fit. All three give the same support. The difference lies in the minimum and maximum clearance. 

A drill bit is necessary when driving a clearance hole, as discussed in one of the sections above. It may look like a small part of the entire process, but it reshapes everything. A screw and a drill bit are foundational materials in starting a project. Without the proper foundation, you will unlikely get the results you want.

Let’s say you arrived at the store to purchase your very first drill bit. You find out there are several sizes available. So you ask yourself a question, “What drill bit to use for screw size?”. It should have the same size as the screw’s shaft, excluding the threads. To get an estimate, put the screw and drill bit beside each other. If they are similar, that is the bit size to go. Alternately, you can check the measurements in the packaging to confirm.

Here are a few tips to consider:

Tap and Clearance Drill Sizes

Now you know how to choose the correct bit for every screw, it is time to make the pilot hole. It serves as a guide for where the screw needs to go while minimizing breaking and chipping. Here are some steps to follow:

Below are some frequently asked questions regarding the drill bit and tap size chart.

A 1/4 drill bit is 7mm or 0.2756m in metric size. 

The standard drill sizes come in 1/4 inches, 3/8 inches, and 1/2 inches for home use. 5/8 inches and 3/4 inches are also available but are usually for industrial and heavy-duty drills.

Use a # 25 drill bit size. Its fractional equivalent is 5/32 inches, and its decimal equivalent is 0.1495 inches. 

The diameter is 0.19 inches or 4.826mm. 

Below are the steps to take when finding the right one to use for a particular screw size.

How to find out what drill bit to use for a screw size

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