MAN4MACHINE4-8 UNJ
Unified National J-Series (Aerospace Root Radius)
The inch-system counterpart to ISO metric MJ threads (see iso.man4machine.com): the same 60 degree Unified profile, with a larger and more strictly controlled root radius than UNR, built for aerospace fasteners that see repeated load cycling over the life of an airframe.
- Standard
- ASME B1.1
- Flank angle
- 60° included
- TPI
- 8
- Major diameter
- 4.0000" (basic)
Thread profile
A 60 degree included flank angle, with a controlled root radius rather than a flat or unspecified root -- the fatigue-resistant detail this diagram's rounded root stands in for.
Basic major 4.0000", pitch diameter 3.9188", minor diameter 3.8647" -- theoretical dimensions before any tolerance class is applied.
UNJ sizes
| Size | TPI | Major Ø | Pitch Ø | Minor Ø |
|---|---|---|---|---|
| 1 | 8 | 1.0000" | 0.9188" | 0.8647" |
| 1 | 12 | 1.0000" | 0.9459" | 0.9098" |
| 1-1/8 | 8 | 1.1250" | 1.0438" | 0.9897" |
| 1-1/8 | 12 | 1.1250" | 1.0709" | 1.0348" |
| 1-1/4 | 8 | 1.2500" | 1.1688" | 1.1147" |
| 1-1/4 | 12 | 1.2500" | 1.1959" | 1.1598" |
| 1-3/8 | 8 | 1.3750" | 1.2938" | 1.2397" |
| 1-3/8 | 12 | 1.3750" | 1.3209" | 1.2848" |
| 1-1/2 | 8 | 1.5000" | 1.4188" | 1.3647" |
| 1-1/2 | 12 | 1.5000" | 1.4459" | 1.4098" |
| 1-3/4 | 8 | 1.7500" | 1.6688" | 1.6147" |
| 1-3/4 | 12 | 1.7500" | 1.6959" | 1.6598" |
| 2 | 8 | 2.0000" | 1.9188" | 1.8647" |
| 2 | 12 | 2.0000" | 1.9459" | 1.9098" |
| 2-1/4 | 8 | 2.2500" | 2.1688" | 2.1147" |
| 2-1/4 | 12 | 2.2500" | 2.1959" | 2.1598" |
| 2-1/2 | 8 | 2.5000" | 2.4188" | 2.3647" |
| 2-1/2 | 12 | 2.5000" | 2.4459" | 2.4098" |
| 2-3/4 | 8 | 2.7500" | 2.6688" | 2.6147" |
| 2-3/4 | 12 | 2.7500" | 2.6959" | 2.6598" |
| 3 | 8 | 3.0000" | 2.9188" | 2.8647" |
| 3 | 12 | 3.0000" | 2.9459" | 2.9098" |
| 3-1/4 | 8 | 3.2500" | 3.1688" | 3.1147" |
| 3-1/2 | 8 | 3.5000" | 3.4188" | 3.3647" |
| 4 | 8 | 4.0000" | 3.9188" | 3.8647" |
Did you know
The J is for jet age fatigue
UNJ threads (and their metric counterpart, ISO MJ -- see iso.man4machine.com) exist because a sharp or poorly controlled thread root is exactly where a fatigue crack starts under repeated load. Aerospace fasteners cycle through thousands of takeoffs, pressurizations, and landings, so UNJ specifies a larger, tightly controlled root radius purely to buy fatigue life a standard UN thread's root doesn't guarantee.
Tap drill calculator
Try “1/4-20 UNC-2A”, “#10-32 UNF”, or “1-8 UN-3A”. Add “LH” for a left-hand thread.
Basic (theoretical) dimensions and a shop tap drill only -- ASME B1.1's exact Class 1A/2A/3A pitch diameter limits depend on length of thread engagement as well as grade. Consult the standard or a calibrated thread gauge for gauge-critical work.
Calculated live
Basic dimensions
- Major diameter
- 4.0000"
- Pitch diameter
- 3.9188"
- Minor diameter
- 3.8647"
Clearance (normal)
- Clearance drill
- 2" (4.0313")
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