M5 tap drill size and thread dimensions
M5 has a major diameter of 5.000 mm and a pitch of 0.8 mm. Every other dimension below follows from those two numbers and the 60-degree thread form.
- Clearance hole
- 5.400
- Pitch diameter
- 4.4804
- Minor diameter of the nut thread
- 4.1340
- Minor diameter of the bolt thread
- 4.0185
- Tensile stress area
- 14.183 mm2
- Breaking load at that tensile strength
- 11 346
- The old "diameter minus pitch" drill
- 4.200
- Engagement that rule actually gives
- 92.4 %
- Threads engaged over that length
- 9.38
- Equivalent threads per inch
- 31.750
Show the working
- Thread engagement = 75
- Clearance hole allowance = 8
- Length of engagement = 7.5
- Material tensile strength = 800
- major = 5 = 5
- p = 0.8 = 0.8
- h = 0.8 * 0.8660254037844386 = 0.692 82
- Tap drill = 5 - 75/100 * 1.082532 * 0.8 = 4.350 48
- The old "diameter minus pitch" drill = 5 - 0.8 = 4.2
- Engagement that rule actually gives = 100 / 1.082532 = 92.376
- Pitch diameter = 5 - 0.649519 * 0.8 = 4.480 38
- Minor diameter of the nut thread = 5 - 1.082532 * 0.8 = 4.133 97
- Minor diameter of the bolt thread = 5 - 1.226869 * 0.8 = 4.0185
- Tensile stress area = pi/4 * (5 - 0.938194 * 0.8)^2 = 14.1825
- Clearance hole = 5 * (1 + 8/100) = 5.4
- Breaking load at that tensile strength = 14.1825 * 800 = 11 346
- shear_area = pi * 4.133 97 * 7.5 * (0.5 + 0.57735 * (4.480 38 - 4.133 97)/0.8) = 73.0534
- Threads engaged over that length = 0.8 > 0 ? 7.5 / 0.8 : 0 = 9.375
- Equivalent threads per inch = 0.8 > 0 ? 25.4 / 0.8 : 0 = 31.75
Values are shown to six significant figures here; the arithmetic itself runs on exact fractions and is only rounded where a number is printed.
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The formula
- tap drill = D - (engagement / 100) x 1.082532 x P
- pitch diameter = D - 0.649519 P
- internal minor diameter = D - 1.082532 P
- tensile stress area = (pi/4)(D - 0.938194 P)^2
The familiar "drill equals diameter minus pitch" rule actually produces about 92% thread engagement, not 75%. Past roughly 75% the extra holding power is negligible and the tapping torque rises sharply, which is why 75% or even 65% is the shop standard.
The tensile stress area formula is the ISO 898-1 definition, based on the mean of the pitch and minor diameters.
Cut a clearance hole rather than a close fit unless the joint is dowelled: thread clearance is what lets parts line up.
M5 at common engagements
| Engagement | Tap drill (mm) | Tap drill (in) |
|---|---|---|
| 65% | 4.437 | 0.1747 |
| 70% | 4.394 | 0.1730 |
| 75% | 4.350 | 0.1713 |
| 80% | 4.307 | 0.1696 |
| 85% | 4.264 | 0.1679 |
| 90% | 4.221 | 0.1662 |
Pick the nearest drill above the figure, never below it.
Frequently asked
What drill size do I need for M5?
4.35 mm (0.1713 in) for 75% thread engagement. The traditional rule gives 4.20 mm, which is a tighter and harder-tapping hole.
What is the pitch of M5?
0.8 mm.
Where the numbers come from
- Thread geometry follows the ISO 68-1 basic profile shared by ISO metric and Unified inch threads; the stress-area definition is from ISO 898-1.