Standards
Surface Treatments
Certifications
- ISO 9001 - 2015 Certified
- PED 2014/68/EC
- NACE MR0175/ISO 15156-2
- NORSOK M-650
- DFAR
- MERKBLATT AD 2000 W2/W7/W10
NAS1351 close-tolerance 12-point bolts
NAS1351 is the National Aerospace Standard for close-tolerance 12-point external-drive aerospace bolts. It is widely specified by airframe and engine OEMs when shear-pin tolerance matters in attachment fittings, because the close-tolerance shank lets the bolt act as a shear pin while still carrying axial preload through the 12-point head. NAS1351 is typically produced to 160 ksi tensile in A286 (UNS S66286), and is dimensionally interchangeable with MS21250 for most retrofit work, with the close-tolerance shank diameter being the principal difference.
TorqBolt manufactures NAS1351 bolts in A286, AISI 8740 chromoly heat-treated, Inconel 718 and Ti-6Al-4V (Grade 5) to AS9100D Rev D and ISO 9001:2015 quality systems, with NORSOK M-630 and NACE MR0175 / ISO 15156 qualifications for sour-service offshore applications. Each bolt head carries the struck tB manufacturer ligature plus the alloy grade marking, and every lot ships with a mill test report (MTC 3.1 standard, MTC 3.2 critical with third-party witness inspection of chemistry, hardness, tensile, and dimensional records).
Common Alloys for NAS1351
| Alloy | Tensile | Service envelope |
|---|---|---|
| A286 (UNS S66286) | 160 ksi | up to 700 °C |
| Inconel 718 (UNS N07718) | 180 ksi | up to 700 °C, jet-engine |
| AISI 8740 chromoly | up to 220 ksi (HT) | standard high-strength |
| Ti-6Al-4V (Grade 5) | 130 ksi | 56% lighter than steel |
UNJ-3A External Thread Dimensions (Common 12-Point Bolt Sizes)
Per SAE AS8879 (controlled-root-radius UNJ external thread). 12-point aerospace bolts under MS21250, NAS1351, AS3216, NAS6303 to NAS6320 are produced to UNJ-3A external thread tolerances. Root radius 0.150 P to 0.180 P (where P = pitch) for fatigue resistance, this is the difference vs standard UN-3A and the reason aerospace specifies UNJ.
| Nominal | TPI | Pitch P (mm) | Major Dia Min (mm) | Major Dia Max (mm) | Pitch Dia Min (mm) | Pitch Dia Max (mm) | Minor Dia Min (mm) | Minor Dia Max (mm) |
|---|---|---|---|---|---|---|---|---|
| 1/4-28 UNJF-3A | 28 | 0.907 | 6.297 | 6.350 | 5.706 | 5.770 | 5.156 | 5.296 |
| 5/16-24 UNJF-3A | 24 | 1.058 | 7.875 | 7.938 | 7.185 | 7.249 | 6.553 | 6.711 |
| 3/8-24 UNJF-3A | 24 | 1.058 | 9.462 | 9.525 | 8.773 | 8.840 | 8.139 | 8.298 |
| 7/16-20 UNJF-3A | 20 | 1.270 | 11.051 | 11.113 | 10.227 | 10.297 | 9.467 | 9.652 |
| 1/2-20 UNJF-3A | 20 | 1.270 | 12.638 | 12.700 | 11.815 | 11.887 | 11.051 | 11.243 |
| 9/16-18 UNJF-3A | 18 | 1.411 | 14.225 | 14.288 | 13.310 | 13.385 | 12.466 | 12.673 |
| 5/8-18 UNJF-3A | 18 | 1.411 | 15.812 | 15.875 | 14.897 | 14.973 | 14.054 | 14.262 |
| 3/4-16 UNJF-3A | 16 | 1.588 | 18.991 | 19.050 | 17.961 | 18.040 | 17.018 | 17.246 |
| 7/8-14 UNJF-3A | 14 | 1.814 | 22.166 | 22.225 | 21.001 | 21.085 | 19.926 | 20.181 |
| 1-12 UNJF-3A | 12 | 2.117 | 25.336 | 25.400 | 23.974 | 24.064 | 22.717 | 22.985 |
| 1 1/4-12 UNJF-3A | 12 | 2.117 | 31.687 | 31.750 | 30.328 | 30.418 | 29.072 | 29.343 |
| 1 1/2-12 UNJF-3A | 12 | 2.117 | 38.037 | 38.100 | 36.678 | 36.768 | 35.422 | 35.693 |
| 1 15/16-12 UNJF-3A | 12 | 2.117 | 49.149 | 49.213 | 47.791 | 47.886 | 46.535 | 46.812 |
| 2-12 UNJF-3A | 12 | 2.117 | 50.737 | 50.800 | 49.378 | 49.473 | 48.122 | 48.399 |
Internal thread (UNJ-3B, mating nut) tolerances and metric M-J equivalents available on request. Send drawing or spec callout to info@torqbolt.com.
Request a Quote
Send drawing or PO line referencing NAS1351 to info@torqbolt.com or call +91-22-66157017.
Related aerospace specs
For broader 12-point aerospace specification context, see also the parent aerospace fasteners hub and the full 12-point catalog, plus sibling specs:
- MS21250, 160 ksi 12-point external-drive aerospace bolt
- AS3216, 180 ksi superalloy 12-point for turbine section
- MIL-DTL-7838, legacy mil-spec, replaced by NAS series
- NAS6303, 3/16" body NAS 6300-series tension cap-screw
- NAS6304, 1/4" body NAS 6300-series tension cap-screw
- NAS6305, 5/16" body NAS 6300-series tension cap-screw
- NAS6308, 1/2" body NAS 6300-series tension cap-screw
- NAS6310, 5/8" body NAS 6300-series tension cap-screw
- NAS6312, 3/4" body NAS 6300-series tension cap-screw
- NAS6315, 15/16" body NAS 6300-series tension cap-screw
- NAS6320, 1-1/4" body NAS 6300-series tension cap-screw
- DIN 12-Point, European metric 12-point M5 to M30, grade 12.9
Frequently Asked Questions
What does NAS1351 cover?
NAS1351 is the National Aerospace Standard covering close-tolerance 12-point external-wrenching bolts. These bolts are dimensioned for shear-pin fit applications where airframe structural design requires tight tolerance between the bolt shank and hole.
What grip lengths and diameters does NAS1351 cover?
NAS1351 specifies nominal diameters from 1/4 inch through 5/8 inch in standard 1/16-inch grip length increments up to 1.5 inches, with extended grip-length variants for longer assemblies.
What alloys qualify for NAS1351?
A286 (UNS S66286) per AMS 5731 for 160 ksi tensile, AISI 8740 alloy steel per AMS 6322 for 160 ksi, and PH 13-8 Mo (UNS S13800) per AMS 5629 for higher strength applications.
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