Metric Thread Tap Drill

A threaded core hole is a hole into which an internal thread is cut. The core hole must always be slightly smaller than the nominal diameter of the thread to be cut.

As a rule of thumb for the core hole the following applies:

Thread Nominal diameter - Thread pitch = Core hole diameter

Example: Core hole M8

8mm - 1.25 mm = 6.8mm (core hole for M8)

A distinction is made between standard threads and fine threads for the core hole diameter. The table here shows the core hole diameter for metric standard threads. The thread core hole table for fine threads can be found here.

* All information without guarantee.