The tap drill for an M14 x 1.5 thread is a 12.5 mm drill (0.4921 in), which leaves about 77% of full thread with a cutting tap. The ideal hole for 75% thread is 12.54 mm, and 12.5 mm is the nearest standard metric drill.
| Percent of thread | Ideal hole | Nearest drill | Drill size | Thread achieved |
|---|---|---|---|---|
| 50% | 13.03 mm | 13 mm | 13.00 mm / 0.5118 in | 51% |
| 60% | 12.83 mm | 13 mm | 13.00 mm / 0.5118 in | 51% |
| 65% | 12.73 mm | 12.5 mm | 12.50 mm / 0.4921 in | 77% |
| 70% | 12.64 mm | 12.5 mm | 12.50 mm / 0.4921 in | 77% |
| 75% | 12.54 mm | 12.5 mm | 12.50 mm / 0.4921 in | 77% |
Drill sizes are coarse relative to this pitch: the two drills either side of the target are 26 points of thread apart. 12.5 mm (0.4921 in) gives 77% and a stronger but harder-to-tap thread; 13 mm (0.5118 in) gives 51% and less tapping torque. On M14 x 1.5 the choice is mostly about tap life in hard materials.
M14 x 1.5 is used on wheel bolts and lug nuts on many cars, and on hydraulic and coolant fittings. Its basic pitch diameter is 13.03 mm and its tensile stress area is 124.5 mm². A bolt of this size passes through a 15.50 mm normal-fit clearance hole (ISO 273).
Example: M14 x 1.5 at 75% thread
Result: 12.5 mm (0.4921 in), 77% thread
| Major (nominal) diameter | 14.00 mm / 0.5512 in |
|---|---|
| Pitch | 1.5 mm |
| Basic pitch diameter (d − 0.6495·P) | 13.03 mm |
| Basic minor diameter, internal (d − 1.0825·P) | 12.38 mm |
| Tensile stress area | 124.5 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 fine sizes:
Use 12.5 mm (0.4921 in). It leaves 77% of full thread with a cutting tap; the ideal 75% hole is 12.54 mm. For an easier-to-tap 50% thread, 13 mm (0.5118 in) gives 51%.
12.5 mm is 0.4921 in. The nearest inch drill to the 75% target is 1/2" (0.5000 in), which gives 67% thread.
A forming tap needs a bigger hole: 13.34 mm for 65% thread, so drill 13.5 mm (0.5315 in). Forming taps work in ductile metals such as aluminum and mild steel.
For M14 x 1.5, 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 2 uses the same sizes.
124.5 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 1.5 takes 12.5 mm (0.4921 in); M14 x 2 takes 12 mm (0.4724 in). Check the pitch on the drawing before you drill.
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