MS21042 at a glance

MS21042, nut, self-locking, 450 °f, reduced hexagon, reduced height, ring base, non-corrosion resistant steel — MS21042

MS21042 engineering drawing with dimensions — MS21042

Current standard: NASM21042. MS21042 is now controlled by NASM21042 (MS21042M Notice 1). The part numbers do not change: MS21042-02 is still the number on drawings, IPCs and bags, and it is the same part. Order it by that number; the current document is NASM21042.

Specification

Item	Value
Current standard	NASM21042 (part numbers unchanged)
Type	Self-locking nut
Material	Steel: UNS G10350 (AISI C1035) per AMS 5080 or QQ-S-700; UNS G10420 (AISI C1042); UNS G10500 (AISI 1050) per AMS 5085; UNS G40270 (AISI 4027) per ASTM A322; UNS G40370 (AISI 4037) per ASTM A322, A331, A519, A547 or AMS 6300; UNS G86300 (AISI 8630) per AMS 6280, 6355, 6530, 6550; UNS G87400 (AISI 8740) per AMS 6322, 6323, 6325, 6327, 6358. Hardness 40 HRC max.
Strength	Axial strength and wrenching torque per table (test bolts 180,000 psi min)
Locking	All-metal self-locking element (tool mark or distortion permitted in the locking area)

Item	Value
Max. temperature	450 °F
Finish	Cadmium plated per QQ-P-416, Type II, Class 2. Dry-film lubricated nuts per QQ-P-416; type and class optional if the nuts meet the salt spray requirements of QQ-P-416 Type II.
Procurement	MIL-N-25027 (now NASM25027)
Status	Cancelled by Notice 1 (22 Jun 1999) and superseded by NASM21042; part numbers unchanged. Rev. M (6 Jan 1995) supersedes MS21042L (18 Oct 1993).

Dimensions by size

Dimension, in	.0860-56 UNJC-3B	.1120-40 UNJC-3B	.1380-32 UNJC-3B	.1640-32 UNJC-3B	.1900-32 UNJF-3B	.2500-28 UNJF-3B	.3125-24 UNJF-3B	.3750-24 UNJF-3B
A — Ring base diameter, max (ØA)	.167	.206	.244	.290	.330	.420	.520	.620
B — Ring base diameter, min (ØB)	.137	.176	.214	.260	.290	.386	.482	.575
C — Width across wrenching corners, min	.138	.171	.207	.244	.277	.347	.419	.491
D — Countersink / counterbore diameter (ØD)	.106 – .086	.142 – .112	.168 – .138	.194 – .164	.220 – .190	.386 – .250	.482 – .312	.575 – .375
E — Minimum length of each wrenching corner	.045	.050	.055	.060	.065	.090	.120	.125
F — Minimum distance from washer face to start of E	.019	.028	.039	.041	.043	.057	.077	.089
G — Ring base dimension G (see drawing)	.021 – .004	.027 – .005	.031 – .006	.031 – .006	.031 – .006	.036 – .007	.042 – .008	.042 – .008
H — Overall height	.100 – .080	.125 – .103	.141 – .115	.188 – .125	.188 – .154	.219 – .204	.266 – .251	.282 – .267
J — Dimension J, min (see drawing)	.010	.010	.010	.015	.015	.019	.023	.030
W — Width across flats (includes deformation of the locking element)	.127 – .122	.158 – .150	.190 – .181	.221 – .213	.252 – .243	.316 – .304	.378 – .367	.440 – .430
X — Squareness of bearing surface (pitch diameter within X)	.0025	.003	.003	.003	.003	.003	.004	.004

Maximum – minimum as tabulated in MS21042 Rev. M; letters as on the standard's drawing.

Part numbers

Part no.	Size	Axial strength, lb min	Weight, lb/100 max	Wrenching torque test value, in-lb min
MS21042-02	.0860-56 UNJC-3B	660	.020	5
MS21042-04	.1120-40 UNJC-3B	1,110	.050	10
MS21042-06	.1380-32 UNJC-3B	1,670	.080	20
MS21042-08	.1640-32 UNJC-3B	2,490	.150	30
MS21042-3	.1900-32 UNJF-3B	3,470	.180	60
MS21042-4	.2500-28 UNJF-3B	6,200	.350	150
MS21042-5	.3125-24 UNJF-3B	9,820	.600	330
MS21042-6	.3750-24 UNJF-3B	15,200	.800	530

Every part number of MS21042 Rev. M, each with its own link. Codes (material, finish) build the full number in the box below.

Part number

What each code means

Part	Meaning
Format	MS21042{lube}<dash>
-	Lube: Not dry-film lubricated (no letter; the hyphen precedes the dash number)
L	Lube: Dry-film lubricated (letter L before the first dash number)
Example	MS21042L4 — .2500-28 nut, cadmium plated, dry-film lubricated. MS21042-4 is the same nut, cadmium plated, not dry-film lubricated.

Notes from the standard

Threads before lubrication per MIL-S-8879 (UNJC for dash -02 to -08, UNJF for -3 to -6).
Design of the wrenching pad faces between corners is optional if the corners are within the limits of E, W and C before lubrication.
Manufacturer's identification is required for sizes .1640-32 and larger; for .1380-32 and smaller it is at the manufacturer's option.
Nuts shall be used in accordance with the limitations of MS33588.
Nuts shall be tested for wrenching torque with a box or socket wrench.
In the Rev. M sheet the ØD maximum for dash -4, -5 and -6 is printed equal to the ØB minimum (.386, .482, .575); this looks like a typographical error, since the equivalent MS21043E values are .280, .342 and .405.
Interchangeability (Table II): AN363, AN364, AN365, MS20364, MS20365 and MS21040 and parts of NAS679, NAS1021, NAS1022 and NAS1291 are replaced by MS21042 -02 to -6; the size 7 and larger nuts in those documents go to NAS679 or MS21245.
Dimensions in inches; remove all sharp edges and burrs; surface texture 125 microinches max.
Figures are read from a low-resolution scan.

Sources

MS21042 Rev. M, 6 Jan 1995 — Nut, Self-Locking, 450 °F, Reduced Hexagon, Reduced Height, Ring Base, Non-Corrosion Resistant Steel — dimensions, part numbers and notes. Public domain, distribution unlimited. Notices: Notice 1 (22 Jun 1999): MS21042M cancelled and superseded by NASM21042; the part numbers are identical and have not been changed (example MS21042-02).

Educational reference only. not approved data. Always consult the applicable SRM, AMM, or AC 43.13-1B and your certifying authority.