The tap drill for an M14 x 2 thread is a 12 mm drill (0.4724 in), which leaves about 77% of full thread with a cutting tap. The ideal hole for 75% thread is 12.05 mm, and 12 mm is the nearest standard metric drill.
| Percent of thread | Ideal hole | Nearest drill | Drill size | Thread achieved |
|---|---|---|---|---|
| 50% | 12.70 mm | 12.5 mm | 12.50 mm / 0.4921 in | 58% |
| 60% | 12.44 mm | 12.5 mm | 12.50 mm / 0.4921 in | 58% |
| 65% | 12.31 mm | 12.5 mm | 12.50 mm / 0.4921 in | 58% |
| 70% | 12.18 mm | 12 mm | 12.00 mm / 0.4724 in | 77% |
| 75% | 12.05 mm | 12 mm | 12.00 mm / 0.4724 in | 77% |
Drill sizes are coarse relative to this pitch: the two drills either side of the target are 19 points of thread apart. 12 mm (0.4724 in) gives 77% and a stronger but harder-to-tap thread; 12.5 mm (0.4921 in) gives 58% and less tapping torque. On M14 x 2 the choice is mostly about tap life in hard materials.
M14 shows up on heavy machinery, older automotive parts and some agricultural equipment; it is less common than M12 or M16. Its basic pitch diameter is 12.70 mm and its tensile stress area is 115.4 mm². A bolt of this size passes through a 15.50 mm normal-fit clearance hole (ISO 273).
Example: M14 x 2 at 75% thread
Result: 12 mm (0.4724 in), 77% thread
| Major (nominal) diameter | 14.00 mm / 0.5512 in |
|---|---|
| Pitch | 2 mm |
| Basic pitch diameter (d − 0.6495·P) | 12.70 mm |
| Basic minor diameter, internal (d − 1.0825·P) | 11.83 mm |
| Tensile stress area | 115.4 mm² |
| Fit | Hole diameter |
|---|---|
| Close | 15.00 mm / 0.5906 in |
| Normal | 15.50 mm / 0.6102 in |
| Loose | 16.50 mm / 0.6496 in |
All Metric coarse sizes:
Use 12 mm (0.4724 in). It leaves 77% of full thread with a cutting tap; the ideal 75% hole is 12.05 mm. For an easier-to-tap 50% thread, 12.5 mm (0.4921 in) gives 58%.
12 mm is 0.4724 in. The nearest inch drill to the 75% target is 15/32" (0.4688 in), which gives 81% thread.
A forming tap needs a bigger hole: 13.12 mm for 65% thread, so drill 13 mm (0.5118 in). Forming taps work in ductile metals such as aluminum and mild steel.
For M14 x 2, ISO 273 gives close fit 15.00 mm, normal fit 15.50 mm and loose fit 16.50 mm. The hole depends only on the diameter, so M14 x 1.5 uses the same sizes.
115.4 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. M14 x 2 takes 12 mm (0.4724 in); M14 x 1.5 takes 12.5 mm (0.4921 in). Check the pitch on the drawing before you drill.
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