Least Material Condition
The NAS1291 series is known as a thin walled, high strength nut. The drawing below illustrate the wall thickness of the NAS1291 series as compared to nuts of the same thread diameter. It should be noted that NAS1291-02 thru NAS1291-6 were superseded by NASM21042 which are dimensional the same. For comparisons of these sizes please visit MS21042.info.
| Thread Diameter | NAS1291 lock-nuts | NAS1804 lock-nuts | NAS1291C lock-nuts | MS21044N lock-nuts |
| .4375" |  |
 |
 |
 |
| NAS1291-7 | NAS1804-7 | NAS1291C7 | MS21044N7 | |
| .5000" |  |
 |
 |
 |
| NAS1291-8 | NAS1804-8 | NAS1291C8 | MS21044N8 | |
| .5625" |  |
 |
 |
 |
| NAS1291-9 | NAS1804-9 | NAS1291C9M | MS21044N9 | |
| .6250" |  |
|
 |
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| NAS1291-10 | NAS1804-10 | NAS1291C10 | MS21044N10 |
Below are downloadable PDFs of all of the LMC drawings above:
NAS1291X | Cadmium Plated without Lubricant
NAS1291 | Cadmium Plated, Dry File Lubricated
NAS1291C | Stainless A286, Silver Plated, without Lubricant
MS21044N Series | A hexagonal self-locking nut with nylon insert
NAS1804 Series | 12 point lock-nut, which is dimensionally similar to the MS21042 series. Made of alloy steel and cadmium plated
NAS1805 Series | Dimensionally the same as the NAS1804, only made of A286. May be cadmium or silver plated, and with or without lubricant.
The NAS1291 series are dimensionally the same as the MS21042 series, with the addition of larger thread diameters up to .6250" . NAS1291-02 thru -6 are inactive for design, and have been superseded by NASM21042. NAS1291C04 thru C6 were superseded by NASM21043:
MS21042 Series | Cadmium Plated Steel-Alloy Lock-Nut
MS21042L Series | 'L' - Dry Film Lubricated
MS21043 Series | Dimensionally the same as MS21042, only made of stainless
Past Revisions | Historical
Previous revisions of the NAS1291 are under copyright and thus cannot be provided by NAS1291.info. However, past revisions of the military standard of MS21042 series lock-nuts can be found on everyspec.com. These nuts are dimensionally the same:
MS21042 Drawing Revision M, 1993
It has been discussed in the aerospace community that NAS1291 & MS21042 lock nuts were originally specified with a maximum tension of 125 KSI. While NAS1291.info has be unable to locate an original print to verify this claim, we have found a document that supports it. Below is a Service News issue from Lockheed on Fasteners found in the C-130:
Downloads
The prints found here within are not to be used for the manufacturer, procurement, or use of NAS1291 hardware. They are for educational proposes only. The most current revision can be found on IHS Global , and are the property of the AIA.