Learn · Which spec replaces which

MS20470 vs MS20426 vs NAS1097 solid rivet heads

These are three head styles. No public document read for this page says one replaces another. MS20470 is the universal (protruding) head. MS20426 is the 100° countersunk head. NAS1097 is a 100° flush shear head, and MIL-HDBK-5J lists a lower reference head height for it than for MS20426: 0.037 in against 0.055 in at 5/32 diameter.[1][2][3][4]

Head

MS20470
Universal head[1]
MS20426
Countersunk 100° precision head[2]
NAS1097
100° flush shear head[3][5]

Head height (ref.) at 1/8, 5/32, 3/16, 1/4 dia, 7050-T73 rivet

MS20470
Protruding head. Not in these countersunk tables.
MS20426
MS20426E: 0.042, 0.055, 0.070, 0.095 in[4]
NAS1097
NAS1097-E: 0.029, 0.037, 0.046, 0.060 in[4]

Document

MS20470
MS20470H cancelled 18 August 1998, superseded by NASM20470. Part numbers not changed.[1]
MS20426
MS20426L cancelled 18 August 1998, superseded by NASM20426. Part numbers not changed.[2]
NAS1097
National Aerospace Standard, adopted by the Department of Defense on 9 March 1989.[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 say3
  • MIL-HDBK-5J, section 9.2.4.6.3: "In the sheet critical range, fasteners with different head shapes, head sizes (NAS 1097, MS 29694, or MS 20426), material, or heat treatment will be considered different fasteners and will require separate tests."[4]
  • FAA AC 43.13-1B, para 4-57b: "Rivets may not be replaced by a type having lower strength properties, unless the lower strength is adequately compensated by an increase in size or a greater number of rivets."[3]
  • Same paragraph: "Replace rivets with those of the same size and strength whenever possible."[3]
More from the documents3
  • The head heights come from two MIL-HDBK-5J joint strength tables for 7050-T73 (E) rivets in machine-countersunk sheet: Table 8.1.2.2(n) for NAS1097-E in clad 2024-T3 and clad 7075-T6, and Table 8.1.2.2(s) for MS20426E in clad 7075-T6. The handbook marks the head heights as reference values. The joint strength values in the two tables differ by sheet thickness and are not reproduced here.[4]
  • MIL-HDBK-5J foreword: "This handbook is for guidance only." It also says the handbook "will be superseded" by the MMPDS Handbook, which SpecLok has not read.[4]
  • AC 43.13-1B says the universal head rivet may be used as a replacement for roundhead, flathead and brazier head rivets. It does not say that about countersunk heads.[3]
Not in a public source3
  • NAS1097 head diameter, tolerances and material codes (AIA document, not read).
  • Any statement that NAS1097 may be installed in place of MS20426 or MS20470, or the reverse. None was found in a public document.
  • MMPDS, the current successor to MIL-HDBK-5J, is sold and was not read.
Sources5

Sources

5

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. MS20470H Notice 1 (18 August 1998) (Department of Defense)
  2. MS20426L Notice 1 (18 August 1998) (Department of Defense)
  3. FAA AC 43.13-1B (Change 1) (FAA)
  4. MIL-HDBK-5J (31 January 2003) (Department of Defense)
  5. NAS1097 DoD adoption notice (DLA ASSIST)

Get the part quoted

Enter the part number your drawing, IPC or engineering order calls out. SpecLok collects quotes with price, lead time and certs.