M52 tap drill size and thread dimensions
M52 has a major diameter of 52.000 mm and a pitch of 5.0 mm. Every other dimension below follows from those two numbers and the 60-degree thread form.
- Clearance hole
- 56.160
- Pitch diameter
- 48.7524
- Minor diameter of the nut thread
- 46.5873
- Minor diameter of the bolt thread
- 45.8657
- Tensile stress area
- 1757.834 mm2
- Breaking load at that tensile strength
- 1 406 268
- The old "diameter minus pitch" drill
- 47.000
- Engagement that rule actually gives
- 92.4 %
- Threads engaged over that length
- 15.60
- Equivalent threads per inch
- 5.080
Show the working
- Thread engagement = 75
- Clearance hole allowance = 8
- Length of engagement = 78
- Material tensile strength = 800
- major = 52 = 52
- p = 5 = 5
- h = 5 * 0.8660254037844386 = 4.330 13
- Tap drill = 52 - 75/100 * 1.082532 * 5 = 47.9405
- The old "diameter minus pitch" drill = 52 - 5 = 47
- Engagement that rule actually gives = 100 / 1.082532 = 92.376
- Pitch diameter = 52 - 0.649519 * 5 = 48.7524
- Minor diameter of the nut thread = 52 - 1.082532 * 5 = 46.5873
- Minor diameter of the bolt thread = 52 - 1.226869 * 5 = 45.8657
- Tensile stress area = pi/4 * (52 - 0.938194 * 5)^2 = 1757.83
- Clearance hole = 52 * (1 + 8/100) = 56.16
- Breaking load at that tensile strength = 1757.83 * 800 = 1 406 270
- shear_area = pi * 46.5873 * 78 * (0.5 + 0.57735 * (48.7524 - 46.5873)/5) = 8561.97
- Threads engaged over that length = 5 > 0 ? 78 / 5 : 0 = 15.6
- Equivalent threads per inch = 5 > 0 ? 25.4 / 5 : 0 = 5.08
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.
M52 at common engagements
| Engagement | Tap drill (mm) | Tap drill (in) |
|---|---|---|
| 65% | 48.482 | 1.9087 |
| 70% | 48.211 | 1.8981 |
| 75% | 47.941 | 1.8874 |
| 80% | 47.670 | 1.8768 |
| 85% | 47.399 | 1.8661 |
| 90% | 47.129 | 1.8555 |
Pick the nearest drill above the figure, never below it.
Frequently asked
What drill size do I need for M52?
47.94 mm (1.8874 in) for 75% thread engagement. The traditional rule gives 47.00 mm, which is a tighter and harder-tapping hole.
What is the pitch of M52?
5.0 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.