The tap drill for an M16 x 2 thread is a 14 mm drill (0.5512 in), which leaves about 77% of full thread with a cutting tap. The ideal hole for 75% thread is 14.05 mm, and 14 mm is the nearest standard metric drill.
| Percent of thread | Ideal hole | Nearest drill | Drill size | Thread achieved |
|---|---|---|---|---|
| 50% | 14.70 mm | 14.5 mm | 14.50 mm / 0.5709 in | 58% |
| 60% | 14.44 mm | 14.5 mm | 14.50 mm / 0.5709 in | 58% |
| 65% | 14.31 mm | 14.5 mm | 14.50 mm / 0.5709 in | 58% |
| 70% | 14.18 mm | 14 mm | 14.00 mm / 0.5512 in | 77% |
| 75% | 14.05 mm | 14 mm | 14.00 mm / 0.5512 in | 77% |
Drill sizes are coarse relative to this pitch: the two drills either side of the target are 19 points of thread apart. 14 mm (0.5512 in) gives 77% and a stronger but harder-to-tap thread; 14.5 mm (0.5709 in) gives 58% and less tapping torque. On M16 x 2 the choice is mostly about tapping torque and machine power.
M16 is used for structural steel connections, heavy machine bases, press tooling and lifting equipment. Its basic pitch diameter is 14.70 mm and its tensile stress area is 156.7 mm². A bolt of this size passes through a 17.50 mm normal-fit clearance hole (ISO 273).
Example: M16 x 2 at 75% thread
Result: 14 mm (0.5512 in), 77% thread
| Major (nominal) diameter | 16.00 mm / 0.6299 in |
|---|---|
| Pitch | 2 mm |
| Basic pitch diameter (d − 0.6495·P) | 14.70 mm |
| Basic minor diameter, internal (d − 1.0825·P) | 13.83 mm |
| Tensile stress area | 156.7 mm² |
| Fit | Hole diameter |
|---|---|
| Close | 17.00 mm / 0.6693 in |
| Normal | 17.50 mm / 0.6890 in |
| Loose | 18.50 mm / 0.7283 in |
All Metric coarse sizes:
Use 14 mm (0.5512 in). It leaves 77% of full thread with a cutting tap; the ideal 75% hole is 14.05 mm. For an easier-to-tap 50% thread, 14.5 mm (0.5709 in) gives 58%.
14 mm is 0.5512 in. The nearest inch drill to the 75% target is 35/64" (0.5469 in), which gives 81% thread.
A forming tap needs a bigger hole: 15.12 mm for 65% thread, so drill 15 mm (0.5906 in). Forming taps work in ductile metals such as aluminum and mild steel.
For M16 x 2, ISO 273 gives close fit 17.00 mm, normal fit 17.50 mm and loose fit 18.50 mm. The hole depends only on the diameter, so M16 x 1.5 uses the same sizes.
156.7 mm², from As = π/4 × (d − 0.9382 × P)². Multiply it by the bolt material's proof or tensile strength to get the load the thread can carry.
No. The drill depends on the pitch, not only the diameter. M16 x 2 takes 14 mm (0.5512 in); M16 x 1.5 takes 14.5 mm (0.5709 in). Check the pitch on the drawing before you drill.
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