Most 8mm taps are 8mm x 1.25, and the standard tap drill for that thread is 6.8mm, close to 17/64″ if you only have fractional bits. An M8 × 1.25 tap and 6.8mm drill bit set gives you both.
Finer 8mm x 1.0 taps need a slightly bigger hole, so I list both, along with how to convert metric bit sizes to inches.
Contents · 7 sections
What Size Drill Bit For 8mm Tap?
For an 8mm tap, use a 6.8mm drill bit for the standard 8mm x 1.25 thread. In the American system, the closest size is around 17/64″ or 0.265 inches.
What is an 8mm Drill Bit Converted to Inches?
An 8mm drill bit is approximately 0.315 inches.
| Tap size | Drill bit size |
| 8mm | 17/64” |
There are two different tap sizes within the 8mm range. Because of this, the drill bit sizes will differ from one another. The 17/64” drill bit is based on the measurements of a 8mm x 1.25 tap.
If you want to go by metric measurements, that’s 6.8mm. If you’re using a finer 8mm x 1.0 tap, use a 7.0mm drill bit.
| Tap Size (and Type) | Drill bit size |
| 8mm x 1.25 tap | 17/64” (or 6.8mm) |
| 8mm x 1.0 tap | 7.0mm |
How to use 8mm Tap
If you don’t have one yet, consider purchasing a drill and tap set that will fit your budget. Make sure it has the ability to fit drill bits like the 8mm tap. Another thing you need to remember is the type of tap you plan on using.
Remember, the drill bit size will differ between a 8mmx 1.25 and a 8mm x 1.0 tap. Choosing the wrong size may not bode well for your planned project. You want everything to fit perfectly whether you are using a screw or a bolt.
When using taps, you are using it to drill through pieces of metal. Before drilling, you’ll want to make sure of a few things. One, make sure the piece you are drilling is clamped down securely.
It should be on a vise or a C-clamp. You want it to be stable so the hole you drill is perfect straight through. If the piece of metal moves ever so slightly, the hole may be a little crooked and make it a challenge to install a screw or bolt.
Once the drill bit is installed (or the tap), you can drill a hole through the metal. Keep in mind that you will need to use a drill bit that is not a standard bit like you would normally use. The best drill bits for metal are either a titanium or cobalt tap drill bit since they have a better chance at cutting through steel.
If you are new to working with metals, it would be smart to use a center punch to create pre-drilled divots. This will help you determine where you plan on drilling holes. Whether it’s creating hinges for doors or assembling a steel frame for tables, it’s always good to pre-determine where the holes need to be drilled for bolts and screws.
Another thing that you don’t want to forget is drilling oil. Lubricating the holes (pre-drilled or already drilled) will make the job a whole lot easier. You want the installation of your screws or bolts to be nice and smooth.
When to use 8mm Tap
The only time when you are using an 8mm tap (or any tap for that matter), is when you are working with metal. A couple of the best types of metal that DIY-ers and professionals use are steel and aluminum.
At this point, you should be able to choose a tap that is made from either cobalt or titanium. The former is considered one of the most popular choices due to its durability and quick heat dissipation. You can use an 8mm tap if you are drilling small holes that are threaded for screws and bolts.
Other Considerations For 8mm Tap
If you are using small pieces of metal, it would be ideal to use a handheld drill. Corded or cordless, either one will do just fine. It may not require a lot of power, but it should be fast enough to where you can create threaded holes.
Also, you’ll want to determine the size screws that you want to use. In this instance, you’ll either be using 8mm (diameter) screws. Specifically, look for sizes like M8 x 1.25 or M8 x 1 screws since they are the closest that you can get to screws that can fit threaded holes.
If needed, you can also consider going up a size to a 10mm tap drill bit size.
You can also consider whether you can use a drill for your tap drill bit or using a T-handle and creating threaded holes manually. It will depend on the project you are doing and how much time you plan on investing in it overall.
Before Using a 8mm Tap
Before using a tap, please use any safety gear since you’ll be working with metal. You may encounter small pieces of metal shavings that may have rough edges and can cause cuts. Be sure to blow away any metal shavings from the holes.
Clean the inside of the threaded holes with a small wire brush before installing any screws or bolts. This will ensure that the installation process is smooth and seamless.
Final Thoughts
An 8mm tap is quite small, and it can be useful for your small metal projects like forging when you want to quickly drill such holes. Whether it’s for door hinges or something else, it’s very useful to have.
Finding the right drill bit for an 8mm tap doesn’t have to be a challenge. But once you are able to find one, you’ll be able to get right to work with some of your planned projects. I hope that this guide has been a big help for you.
Just find the right drill bit and get started on that project you’ve been planning. You’ll be more than happy once the finished product is completed.
