M48 tap drill size and thread dimensions
M48 has a major diameter of 48.000 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
- 51.840
- Pitch diameter
- 44.7524
- Minor diameter of the nut thread
- 42.5873
- Minor diameter of the bolt thread
- 41.8657
- Tensile stress area
- 1473.149 mm2
- Breaking load at that tensile strength
- 1 178 520
- The old "diameter minus pitch" drill
- 43.000
- Engagement that rule actually gives
- 92.4 %
- Threads engaged over that length
- 14.40
- Equivalent threads per inch
- 5.080
Show the working
- Thread engagement = 75
- Clearance hole allowance = 8
- Length of engagement = 72
- Material tensile strength = 800
- major = 48 = 48
- p = 5 = 5
- h = 5 * 0.8660254037844386 = 4.330 13
- Tap drill = 48 - 75/100 * 1.082532 * 5 = 43.9405
- The old "diameter minus pitch" drill = 48 - 5 = 43
- Engagement that rule actually gives = 100 / 1.082532 = 92.376
- Pitch diameter = 48 - 0.649519 * 5 = 44.7524
- Minor diameter of the nut thread = 48 - 1.082532 * 5 = 42.5873
- Minor diameter of the bolt thread = 48 - 1.226869 * 5 = 41.8657
- Tensile stress area = pi/4 * (48 - 0.938194 * 5)^2 = 1473.15
- Clearance hole = 48 * (1 + 8/100) = 51.84
- Breaking load at that tensile strength = 1473.15 * 800 = 1 178 520
- shear_area = pi * 42.5873 * 72 * (0.5 + 0.57735 * (44.7524 - 42.5873)/5) = 7224.77
- Threads engaged over that length = 5 > 0 ? 72 / 5 : 0 = 14.4
- 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.
Scenarios & local history
Compare a saved scenario
Recent calculations
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.
M48 at common engagements
| Engagement | Tap drill (mm) | Tap drill (in) |
|---|---|---|
| 65% | 44.482 | 1.7513 |
| 70% | 44.211 | 1.7406 |
| 75% | 43.941 | 1.7299 |
| 80% | 43.670 | 1.7193 |
| 85% | 43.399 | 1.7086 |
| 90% | 43.129 | 1.6980 |
Pick the nearest drill above the figure, never below it.
Frequently asked
What drill size do I need for M48?
43.94 mm (1.7299 in) for 75% thread engagement. The traditional rule gives 43.00 mm, which is a tighter and harder-tapping hole.
What is the pitch of M48?
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.