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MS21042 vs AN365, MS20365 and MS21044 self-locking nuts

AN365 was cancelled in 1958 and superseded by MS20365. MS20365 was cancelled in 1966. The MS21044 sheet says MS21044 nuts can replace both in like material, plating and thread size, except 7/16-20, and not the reverse. MS21042 is a different nut (450°F, reduced hexagon, reduced height). Its sheet says it supersedes both, and its table gives a substitute for some all-metal dash numbers and none for others.[1][2][3][4][5][6]

Title

AN365 / MS20365
Nut, self-locking, 250°F[7]
MS21044
Nut, self-locking, hexagon, regular height, 250°F, 125 ksi Ftu and 60 ksi Ftu[8]
MS21042
Nut, self-locking, 450°F, reduced hexagon, reduced height, ring base, non-corrosion resistant steel[6]

Document status

AN365 / MS20365
AN365 cancelled 5 September 1958, superseded by MS20365. MS20365 cancelled 4 November 1966; the DLA record marks it superseded by MS21042. The MS20365 sheet read here is the 1958 revision.[1][2][3]
MS21044
MS21044H cancelled 12 May 1999, superseded by NASM21044. Part numbers not changed.[8]
MS21042
MS21042M cancelled 22 June 1999, superseded by NASM21042. Part numbers not changed.[6]

Width across flats, 1/4-28 (scans print MS21044 and MS21042 values without a decimal point)

AN365 / MS20365
MS20365-428: .438 in (+.002, -.010)[3]
MS21044
MS21044N4: printed 439 max, read as .439 in[4]
MS21042
MS21042-4: printed 316 max, read as .316 in[5]

Axial strength, 1/4-28 steel

AN365 / MS20365
Not in a public source: the MS20365C sheet prints no strength value
MS21044
4,580 lb min[4]
MS21042
6,200 lb min, tested on bolts of 180,000 psi min[5]

This page reports what public documents print. It does not approve a substitution. The aircraft's IPC, SRM or engineering authority decides what may be installed.

Reference only: the controlling drawing, its process spec and the manufacturer's installation instructions govern. How to use these answers

What the notices and sheets say6
  • MS20365C, sheet 1: "INTERCHANGEABILITY RELATION WITH AN365 PARTS: MS20365 PARTS AND AN365 PARTS OF LIKE DASH NUMBER ARE UNIVERSALLY, FUNCTIONALLY AND DIMENSIONALLY INTERCHANGEABLE."[3]
  • MS21044H, note 4, in full up to its last sentence: "MS21044 NUTS CAN UNIVERSALLY REPLACE AN365, MS20365 AND NAS1021 NUTS OF LIKE MATERIAL, PLATING AND THREAD SIZE, EXCEPT FOR AN365 AND MS20365 7/16-20 NUTS. NON-METALLIC INSERT LOCKING DESIGNS CAN BE SUBSTITUTED FOR THE INACTIVATED BRASS OR ALUMINUM ALLOY ALL-METAL LOCKING DESIGN NUTS. AN365, MS20365 AND NAS1021 NUTS CANNOT UNIVERSALLY REPLACE THE MS21044 NUTS." The note then points to MIL-STD-962 for drawing status notes. The scan shows no punctuation between the sentences.[4]
  • MS21042M, note 4: "MS21042 SUPERSEDES AN363, AN364, AN365, MS20364 MS20365 MS21040", and NAS679, NAS1021, NAS1022 and NAS1291 in part.[5]
  • MS21042M Table II is headed "INTERCHANGEABILITY TABLE" and lists "CANCELLED AND INACTIVATED PART NUMBERS" against a substitute. In the AN365 column it gives MS21042-4 for -428C and MS21042-3 for -1032C, and "NONE" for -420C. Every AN365 and MS20365 entry in the table carries the C (all metal) suffix.[5]
  • DLA ASSIST records: AN365, "NUT, SELF&LOCKING, 250 DEG. F (S/S BY MS&20365)", cancelled 5 September 1958. MS20365, "NUT, SELF-LOCKING, 250 DEG. F (ASG) (S/S BY MS21042)", cancelled 4 November 1966. The record prints S/S for superseded.[1][2]
  • Both sheets limit use: "THESE NUTS SHALL BE USED IN ACCORDANCE WITH THE LIMITATIONS OF MS33588".[5][4]
More from the documents4
  • MS20365C suffix letters: "ADD A AFTER DASH NUMBER FOR NUTS HAVING NONMETALLIC INSERTS. ADD C AFTER DASH NUMBER FOR NUTS FABRICATED ENTIRELY FROM METAL."[3]
  • MS21044H Table I lists its dash numbers under a non-metallic insert heading, and the insert material is nylon.[4]
  • FAA AC 43.13-1B: "Fiber or nylon self-locking nuts are not installed in areas where temperatures exceed 250 °F."[7]
  • MS21042M part number examples: MS21042L4 is a .2500-28 nut, cadmium plated, dry film lubricated. MS21042-4 is the same nut not dry film lubricated.[5]
Not in a public source4
  • The AN365 sheet and the cancellation notices for AN365 and MS20365. DLA ASSIST holds a record with the dates but no notice image for either.
  • The current NASM21042 and NASM21044 revisions (AIA documents, not read).
  • MS33588, the usage limits both sheets point to, was not read for this page.
  • Dimensions other than the three across-flats values above were not transcribed. The MS21044H and MS21042M scans drop most decimal points, so the decimal position of those two values is read from the thread size, not from the print.
Sources8

Sources

8

Each number above links to its document. Scanned sheets were read by eye and re-read by OCR; the check script is in the repository under docs/audit-2026-10/reddit-pages.

  1. AN365 document record (DLA ASSIST)
  2. MS20365 document record (DLA ASSIST)
  3. MS20365 Rev C (5 September 1958) (Department of Defense)
  4. MS21044 Rev H (21 September 1993) (Department of Defense)
  5. MS21042 Rev M (6 January 1995) (Department of Defense)
  6. MS21042M Notice 1 (22 June 1999) (Department of Defense)
  7. FAA AC 43.13-1B (Change 1) (FAA)
  8. MS21044H Notice 1 (12 May 1999) (Department of Defense)

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