Let’s start with an important fact–there isn’t just one drill bit size to use for a given tap size. There are several. Moreover, the size recommend...

Imagine the fully formed internal thread. Each thread rises from valley to peak. Now suppose you ran a twist drill down the hole and shaved off som...

Let’s take a closer look at the relationship between torque and thread strength based on thread percentage: Red marks the typical 75% percent of th...

Try this approach, which is based on material and type of work: The material matters because we can afford higher thread engagement in softer mater...

Just one more little wrinkle is that Form Taps (also called “Roll Taps” because they perform thread rolling rather than thread cutting) need a diff...

Well, you can’t use a standard drill chart, that much is clear. You could calculate the optimal size for a particular percentage of thread and then...

Blind Holes are particularly prone to breaking taps. It’s harder to clear the chips for one thing, but the other thing is machinists don’t leave en...

Here you go, Metric and Imperial sizes are called out in the “Use” column in the chart below. It’s even an NPT Tap Drill Chart: