NAS1291 Low-Height Self-Locking Hex Nuts
Hexagon self-locking low-height, lightweight nuts per NAS1291 — dash numbers -02 (.0860-56 UNJC-3B) through -10 (.6250-18 UNJF-3B) in steel for 450°F service (cadmium plate with dry film lubricant) or A286 CRES for 450/800°F (silver plated), with per-size dimensions, weights and minimum axial tensile strengths from the standard sheet.
Last updated: 2026-11
Specifications
NAS1291 is the aerospace answer to "hold a joint in a thin envelope": a hex nut roughly as tall as it needs to be and no more — the standard titles it low height, light weight — with an all-metal locking feature instead of a nylon insert, so the lock survives the temperature classes the standard defines: steel nuts rated 450°F, A286 corrosion-resistant steel nuts available for 450°F (dry film lubricant) or 800°F service (silver plated). The standard sheet runs the full dash-number ladder from -02 (.0860-56 UNJC-3B) through -10 (.6250-18 UNJF-3B) and tabulates, per size: the A width across flats minimum/maximum, B and C envelope minimums, the ØD countersink-relief diameter, the ØF bearing face, H height, J and S geometry limits, ØW maximum, weight per 100 pieces and — the rows aerospace buyers quote — minimum axial tensile strength in pounds, which at -7 (.4375-20) reads 20,600 lbf in steel and 15,450 lbf in A286. Part numbering carries the material and lubrication in the dash suffix: plain dash = steel, cadmium plated with dry film lubricant; X = steel without lubricant; C = A286; M suffix = with approved dry film lubricant. The sheet notes the smallest steel dash numbers (-02 through -6 and their X variants) and C04–C6 are inactive for new design (superseded by NASM21042/NASM21043), and that the -8/-9/-10 nuts are not intended for use with short-thread screws. Steel hardness is capped at Rockwell C49 maximum by the sheet.
| Standard | NAS1291 — nut, self-locking, hexagon, low height, light weight (AIA/NAS part standard, rev 13) |
|---|---|
| Size range | Dash -02 (.0860-56 UNJC-3B) through -10 (.6250-18 UNJF-3B); -02 to -08 coarse UNJC, -3 upward fine UNF per dash table |
| Dimensions at dash -7 (.4375-20 UNJF-3B) | A min/max 0.313/0.328 in; B min/max 0.494/0.504 in; C min 0.562 in; ØD min/max 0.437/0.467 in; ØF min 0.680 in; H min 0.160 in; ØW max 0.708 in |
| Strength at dash -7 | Axial tensile strength minimum 20,600 lbf (steel, 450°F); 15,450 lbf (A286 CRES) |
| Materials & service | Steel 450°F — cadmium plate per AMS-QQ-P-416 class 1 or 2 plus dry film lubricant per NASM25027; A286 CRES — silver plate per AMS2410 for 800°F, or dry film lubricant for 450°F; steel hardness Rockwell C49 max |
| Strength basis | Steel minimum tensile per table based on 160,000 psi (98% of basic pitch diameter area per ASME B1.1, 100% from .3750 up); A286 values based on 125,000 psi per NASM25027 |
| Design notes | Dash -02 through -6 / X02 through X6 and C04–C6 inactive for new design (see NASM21042 / NASM21043); legacy "A" material code inactive — use "C" for A286; -8/-9/-10 not intended for short-thread screws |
| Thread | Dash no. (steel, cad + dry film lube) | Dash no. (steel, unlubricated) | Dash no. (A286, dry film lube) | Dash no. (A286, silver plated) | Dash no. (A286, dry film lube, legacy "A" code) | Dash no. (A286, silver plated, legacy "A" code) | A min (in) | A max (in) | B min (in) | B max (in) | C min (in) | ØD min (in) | ØD max (in) |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| .0860-56 UNJC-3B | 02 | X02 | C02M | C02 | A02M | A02 | .080 | .100 | .122 | .127 | .138 | .086 | .106 |
| .1120-40 UNJC-3B | 04 | X04 | C04M | C04 | A04M | A04 | .103 | .125 | .150 | .158 | .171 | .112 | .142 |
| .1380-32 UNJC-3B | 06 | X06 | C06M | C06 | A06M | A06 | .115 | .141 | .181 | .190 | .207 | .138 | .168 |
| .1640-32 UNJC-3B | 08 | X08 | C08M | C08 | A08M | A08 | .125 | .188 | .213 | .221 | .244 | .164 | .194 |
| .1900-32 UNJF-3B | 3 | X3 | C3M | C3 | A3M | A3 | .154 | .188 | .243 | .252 | .277 | .190 | .220 |
| .2500-28 UNJF-3B | 4 | X4 | C4M | C4 | A4M | A4 | .204 | .219 | .304 | .316 | .347 | .250 | .280 |
| .3125-24 UNJF-3B | 5 | X5 | C5M | C5 | A5M | A5 | .251 | .266 | .367 | .378 | .419 | .312 | .342 |
| .3750-24 UNJF-3B | 6 | X6 | C6M | C6 | A6M | A6 | .267 | .282 | .430 | .440 | .491 | .375 | .405 |
| .4375-20 UNJF-3B | 7 | X7 | C7M | C7 | A7M | A7 | .313 | .328 | .494 | .504 | .562 | .437 | .467 |
| .5000-20 UNJF-3B | 8 | X8 | C8M | C8 | A8M | A8 | .350 | .410 | .556 | .566 | .633 | .500 | .530 |
| .5625-18 UNJF-3B | 9 | X9 | C9M | C9 | A9M | A9 | .420 | .480 | .680 | .692 | .775 | .562 | .592 |
| .6250-18 UNJF-3B | 10 | X10 | C10M | C10 | A10M | A10 | .490 | .550 | .743 | .755 | .846 | .625 | .655 |
| Thread | ØF min (in) | H min (in) | J min (in) | S max (in) | ØW max (in) | Weight (lbs per 100) | Axial tensile strength, steel, lbf min | Axial tensile strength, A286 CRES, lbf min |
|---|---|---|---|---|---|---|---|---|
| .0860-56 UNJC-3B | .137 | .045 | .008 | .0025 | .167 | .02 | 660 | 465 |
| .1120-40 UNJC-3B | .176 | .050 | .010 | .003 | .206 | .05 | 1,110 | 760 |
| .1380-32 UNJC-3B | .214 | .055 | .010 | .003 | .244 | .08 | 1,670 | 1,150 |
| .1640-32 UNJC-3B | .260 | .060 | .015 | .003 | .290 | .15 | 2,490 | 1,720 |
| .1900-32 UNJF-3B | .290 | .065 | .015 | .003 | .330 | .18 | 3,470 | 2,460 |
| .2500-28 UNJF-3B | .386 | .090 | .019 | .003 | .420 | .35 | 6,200 | 4,580 |
| .3125-24 UNJF-3B | .482 | .120 | .023 | .004 | .520 | .60 | 9,820 | 7,390 |
| .3750-24 UNJF-3B | .575 | .125 | .030 | .004 | .620 | .80 | 15,200 | 11,450 |
| .4375-20 UNJF-3B | .680 | .160 | .035 | .005 | .708 | 1.3 | 20,600 | 15,450 |
| .5000-20 UNJF-3B | .786 | .225 | .040 | .005 | .814 | 2.1 | 27,500 | 21,110 |
| .5625-18 UNJF-3B | .874 | .320 | .045 | .006 | .912 | 3.6 | 34,800 | 26,810 |
| .6250-18 UNJF-3B | .976 | .365 | .050 | .007 | 1.014 | 4.5 | 43,600 | 34,130 |
Materials
- Steel (cadmium plated, dry film lubricated)
- A286 CRES (UNS S66286, per AMS5732/AMS5737/AMS5525 chemistry)
Ordering & documentation
Documents
Shipments are backed by Mill Test Certificate (MTC), Dimensional Report, Salt Spray Test Report on request, with full batch traceability from raw material to finished product. Quality management follows the owner-confirmed compliance list: ISO 9001:2015, RoHS, REACH. Exact document sets are confirmed on the order.
Quotation
- The fastener family (NAS1291 Low-Height Self-Locking Hex Nuts) plus the standard designation from your drawing — DIN / ISO / JIS / ASTM / ANSI, or a drawing for custom parts.
- Size (diameter and length), thread type (metric or inch), property class or grade, and coating or finish.
- Quantity per size and your target delivery date.
- Destination country, and any required documents (for example a mill test certificate) so the quote includes them.
Sample & supply
Minimum order quantity is 10,000 pieces. Stock items run 3–7 days. Quantities or variants outside the standard range are confirmed at quotation.
Storage & shipping
Parts are packed for export and shipped factory-direct to buyers in Europe, Asia, the Americas and the Middle East. Store fasteners dry and protected until installation, and keep coated parts in their packaging until use; specific packing and preservation requirements can be stated on the order and confirmed at quotation.
Frequently asked questions
How do I read a NAS1291 part number?
The dash number selects the thread size (-7 is .4375-20 UNJF-3B, for example), and the letter prefix selects material and lubrication: plain dash = steel, cadmium plated with an approved dry film lubricant for 450°F; X prefix = steel without any lubricant coating; C prefix = A286 corrosion-resistant steel, with an M suffix when dry film lubricated (450°F) or silver plated bare for 800°F. The legacy "A" prefix that once designated A286 is inactive for new design — the standard sheet directs new callouts to the "C" code. Note the sheet lists the smallest dash numbers as inactive for new design as well, so a legacy -04 callout should be checked against its superseding NASM part before ordering.
Why choose an all-metal NAS1291 over a nylon-insert lock nut?
Temperature and consistency. A nylon insert loses its locking behaviour as it approaches its softening range and varies with installation speed; the NAS1291 all-metal lock is rated by the standard to 450°F in lubricated steel and 800°F in silver-plated A286, and its locking torque is specified per size (minimum break-away 0.2 in-lb at dash -02 and 0.5 in-lb at dash -04 per the sheet, larger sizes per NASM25027). The costs are a lower re-use count than an elast insert and the need to state the temperature class with the order — the X (unlubricated) and M (lubricated) variants are different parts with different service ratings.
What is the MOQ and lead time for this nut type?
The minimum order quantity is 10,000 pieces. Stock items ship in 3–7 days; non-stock items are confirmed at quotation. Confirm the exact schedule against quantity and size mix at quotation.
Request a Quote
Get factory-direct pricing from the manufacturer.
What to include in your inquiry
- ✓ Standard and property class (e.g. DIN 912, ISO 4762, class 8.8) — or a drawing for custom parts.
- ✓ Sizes, lengths and thread type (metric or inch).
- ✓ Quantity per size and your target delivery date.
- ✓ Destination country, plus any coating or finish requirement.
- ✓ Any documents you need with the shipment (e.g. mill test certificate) so the quote includes them.
- ✓ Your inquiry goes straight to the factory team by email and gets a reply within 24 hours.
- ✓ Factory-direct pricing
- ✓ Standard and custom specifications
- ✓ Factory-direct export to buyers in Europe, Asia, the Americas and the Middle East
- ✓ Full fastener family support