Drill Bit

What Size Drill Bit for a 5/16 Tap?

You will find a suitable drill bit if you ever want to cut through tough materials such as metal. It is not only the size drill bit you need to worry about but also the type of drill bit. The kind of drill bit I recommend for cutting through metal is a tap drill.

If you look at taps, you will find that they come in various sizes. The 5/16 tap is quite common; you can find it in most hardware stores. I recommend you look into it, as it makes it extremely easy to pre-drill holes even in more rigid materials.

To learn more about the 5/16 tap, how to use it, and what size drill bit to use with it, stick around for the rest of this detailed guide. Let's get right into the topic!

Right Drill Bit Size

You can determine what kind of drill bit you need depending on your desired hole size. The tap drill size can vary, but the ideal size is about 17/64''. Sometimes, you will find this number changes to 13/64''. It is always a safe bet to measure everything yourself and note the measurement variations before buying the drill bit.

There are various drill bit sizes and materials on the market, so you should easily find one that will fit your needs. Since you will be drilling in metal, you need the drill bit to be durable and sturdy, not likely to wear out quickly, and not overheat.

You can use this type of drill bit for other DIY projects, not just metal cutting. As for the 5/16 tap drill, you can use it only to make new threads whenever needed. There are 5/16 18, 5/16 24, and 5/16 32 tap sizes suitable for various situations. Depending on which tap size you select, you can decide on the drill bit size.

A general recommendation is to use a drill bit smaller than the tap. I have found that 5/16'' 18 taps pair well with the F-size drill, which is about 0.257 inches in diameter. As for the 5/16'' 24 taps, you should try and pair it with an I-size drill bit, which has a diameter of about 0.272 inches. Both pair well with the 17/64'' drill bit, whereas the 5/16'' 32 pairs best with the 13/64''.

You can find the threads per inch and diameters on the tap and use them to select the suitable drill bit. Consider using the nearest drill bit size if there is no suitable size.

Amount of Pressure

When drilling into any material, you must be very careful with the pressure and speed you use to make the holes. It is vital that with soft materials, you use a limited amount of pressure and operate at a slow speed, at least at the beginning.

When using a 5/16 tap or a 17/64 drill bit, you need to start using a limited amount of pressure. Too much pressure can cause the drill bit to slip or the tap to break after only a short use. Too little pressure can cause a faulty cut into the material, and that might deem the material unusable.

As for the speed, you need to start slowly and gradually increase it as you are near the end of the pre-drilling or drilling. But you should set the drilling speed at a reasonable speed, as that might cause your tap or drill to slip around and cause damage to the material.

To ensure that does not happen, you should create a pilot hole in the material, but more on that in the next section.

Need To Create Pilot Hole

pilot hole

The recommendation to make a pilot hole does not apply only when drilling into metal but also when drilling into all other materials. The pilot hole is very easy to make, but it can help your drill bit stay under control and prevent slips throughout your drilling process.

Pilot holes are the first step toward making a hole in the material. Please mark the spot where you want to drill using a marker. Then, you can make a small indent at that spot with a hammer, but that is not always necessary.

After making the material, you should use a nail or screw to make a small hole. You can use the 5/16 tap to turn the small hole into a larger one and ensure the thread percentage suits the material. When you finish with the tap, you can move on to drilling using a drill bit with the specific measurements I mentioned in the previous sections.

How To Determine the 5/16″ Tap Drill Size?

measuring tape

Tap drill sizes are usually written on the packaging or the tap's specifications list. The manufacturer should always provide accurate measurements. It would make it easy for people to choose between the different drill bit sizes without worrying that they had made a mistake.

Yet, manufacturers sometimes do not list the proper tap size and other variables, so you might need to measure yourself. When doing the measuring, you need to look into both the length and diameter of the tap. Here is how you can determine those measurements:

Tap Length

The length is easier to determine as all you need to do is measure the tap from the head to the end. There can be a slight length difference between tap drills from various manufacturers, so you must ensure that your tap is suitable for the length hole you need to pre-drill into the material.

Tap Diameter

The tap diameter is one of the more difficult things to determine about this tool. You must look at the tap's nominal diameter and thread pitch. No two taps have exactly the same diameter, so you should go ahead and calculate the diameter yourself using the following measuring formula:

DH = DMB - Whole Thread Percentage

DH is going to be the tap drill size as a total. DMB is the nominal diameter you can find when measuring the actual diameter. Then, you would take out the thread percentage or pitch, usually around .0130. You should take the result and round it to the closest drill bit size to determine the drill bit you need for that particular tap drill size.


Thank you for reading this guide on the 5/16 tap and the compatible drill bit sizes for the variations of this tap. Remember to always select a size drill bit closest to the 5/16 tap in diameter and length. You can switch between different-sized drill bits if you need to adjust the hole you drilled into the material.

If you have experience using 5/16 taps or I and F drill bit sizes, please share it with the other readers and me in the comments below. Let me know if you know of any good taps or drill bits that you would recommend to others. I cannot wait to read all your comments!

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