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.

 

Metric Thread Tap Drill Chart

Metric thread

sizes

core hole

(mm)

pitch

regular thread (mm)

M1 0,75 0,25
M1,1 0,85 0,25
M1,2 0,95 0,25
M1,4 1,1 0,30
M1,6 1,3 0,35
M1,8 1,5 0,35
M2 1,6 0,40
M2,2 1,8 0,45
M2,5 2,1 0,45
M3 2,5 0,50
M3,5 2,9 0,60
M4 3,3 0,70
M5 4,2 0,80
M6 5,0 1,00
M7 6,0 1,00
M8 6,8 1,25
M9 7,8 1,25
M10 8,5 1,50
M12 10,2 1,75
M14 12 2,00
M16 14 2,00
M18 15,5 2,50
M20 17,5 2,50
M22 19,5 2,50
M24 21 3,00
M27 24 3,00
M30 26,5 3,50
M36 32 4,00
M42 37,5 4,50
M48 43 5,00
M56 50,5 5,50
M64 58 6,00

* All information without guarantee.