What Size Drill Bit for a ⅜” Tap? [Answered]

Navigating the intricacies of thread tapping can be daunting, especially when it comes to choosing the right drill bit for a ⅜” tap. In my journey as a seasoned DIY enthusiast, I’ve garnered hands-on experience in the technical aspects of such tasks. This article breaks down the essentials, providing you with an easy guide to find the perfect fit for your project.

A ⅜” cap comes in two different thread counts: 16 and 24. Thus, the size of the drill bit is also different for each one of them. A 3/8″ 16 Tap requires a special process, as does a 3/8″ NPT Tap.

Screw Size	Drill Bit	Drill Bit Size
⅜”-16		5/16″
⅜”-24	Q	21/64″

Before moving forward, make sure to test on scrap materials before drilling on actual metal.

Finally, here are guides to drilling through related sizes such as a 1/4″ 20 Tap, 1/2″ Tap, and a 5/8″ Tap.

Concept

The concept behind tapping the threads is not that hard, but the practical approach might be a bit tricky to handle. To get the best results, you need to be careful about:

• In the case of tiny holes, the tapping will extend to the center; thus, screwing the bolt into the hole is a challenging task.
• In case of large holes, the threads will not mate with the bolt.
• In the case of a soft or average material, the tap drill is 75%, but it will be reduced to 50% for tighter connections if the material is hard.
• In the case of hard materials and tighter connections, the recommended drill size is 5/16″ inches.

Here is a table with different sizes of drill bits depending on the number of threads per inch.

Considerations

Here are some considerations that you need to take before drilling a ⅜ tap. It is necessary as the slightest mistake can result in bad accidents.

• Do not forget to pre-decide about what material you are working with, like the size for the drill bit changes depending upon the hardness of the material.
• Try drilling through a scrap piece in the beginning to get a better idea about what you are dealing with.

Drilling And Tapping a 3/8″

Since you are deciding the size of the drill bit, it is time for some action. First, let’s talk about the process of drilling and tapping.

1. Begin with fixing the material between two clamps to avoid any spinning or slipping while you drill. If you miss this step, you might end up injuring yourself.
2. Draw a mark where you want to drill and wear your safety goggles and gloves. It is advised to mask the area with painter’s tape to keep the drill bit in one place.
3. Ensure the drill is perpendicular, as any different angle will create problems in tapping and screwing the bolts.
4. Keep an eye on your drill bit, and it should not get too hot. Do not forget to sharpen the drill bit and use cutting fluid.
5. In the case of hand-held drills, use a drill press or a guide.

Here is the link to a video guide that explains the slightest details about drilling and tapping. This will give a practical understanding of the whole concept.

Using A ⅜” Tap

When you are done drilling a single hole, move on to testing by using a ⅜” tap. It will give you a practical comparison, and it will be apparent if you are headed on the right path.

1. After the drilling is done, start with deburring the edge and removing the sharp edges around the hole.
2. Now add chamfer by using either specialized or normal drill bits to ease out the tapping.
3. Make the extra dust and debris inside or around the hole is thoroughly cleaned.
4. Use a guide while applying pressure on the hole and the material you are working on; otherwise, you can end up with a crooked tap. Make sure you take your time during this critical part.

Here is a link to the study that indicates drilling threaded holes and the whole history behind it.

Pecking

Pecking is defined as one of the methods of tapping threads. This is how it works:

• The principal concept behind pecking is leaning forward to a short distance and then coming back up.
• This process is excellent in protecting your drill bits from overheating, and it makes sure there is no extra torque that triggers the breaking of the material.
• The key point behind this process is that a full turn is used to tap in, but then it is turned half around back.
• Another way to go about pecking is by removing the whole tapping, cleaning the hole, and then going in two turns. The process is supposed to be repeated until the hole is completely tapped.

This is a long process, but it ensures the quality of the tapping.

Frequently Asked Questions

Conclusion 

Even the slightest mistakes can make you end up with crooked tapping, and nobody wants that. Therefore, while tapping, it is essential to be cautious at every step, choose the size of the drill bit carefully depending on the hardness of the material, and never forget to test first and then move forward with the final drilling.