To create our chart, we pulled the basic numbers for the most common threads, class 2B, from the Machinery’s Handbook. To make your search easier, we have created our own Drill Tap Chart that includes only the information that you would most commonly need to properly drill and tap holes. You can also determine your tap drill size by digging into the Machinery’s Handbook, where you will find all of the different classes of threads listed. There are rules of thumb that you can use to calculate the tap drill size you need. This is usually referred to as a tapping drill for the size of the thread that needs to be produced. The most common way to produce an internal thread is to drill a hole and then use a tap to produce the thread.