MS35691E — Plain Hexagon (Jam) Nut: UNC-2B and UNF-2B
Standard: MS35691E | Issued: 23 March 2005 | Supersedes: MS35691D (29 August 1984) | Status: Active for New Design | FSC: 5310 | Unit: Inch-Pound
1. Overview
MS35691E defines the requirements for plain hexagon (jam) nuts with UNC-2B and UNF-2B internal threads, intended for aerospace, military, and industrial applications. The standard covers nominal sizes from 1/4" through 3", five material and finish combinations, and a structured dash number system for part identification. All dimensions are in inches unless otherwise noted.
2. Dimensional Data — Table I
The table below lists key dimensions for each nominal size per MS35691E Table I. Width Across Flats (P), Width Across Corners (G), and Thickness (H) apply to both UNC and UNF thread series for each nominal size.
 |
| Nominal Size / Basic Major Dia. | Width Across Flats P Max (in.) | Width Across Flats P Min (in.) | Width Across Corners G Max (in.) | Width Across Corners G Min (in.) | Thickness H Max (in.) | Thickness H Min (in.) |
|---|---|---|---|---|---|---|
| 1/4 — .2500 | .4375 | .428 | .505 | .488 | .163 | .150 |
| 5/16 — .3125 | .5000 | .489 | .577 | .557 | .195 | .180 |
| 3/8 — .3750 | .5625 | .551 | .650 | .628 | .227 | .210 |
| 7/16 — .4375 | .6875 | .675 | .794 | .768 | .260 | .240 |
| 1/2 — .5000 | .7500 | .736 | .866 | .840 | .323 | .302 |
| 9/16 — .5625 | .8750 | .861 | 1.010 | .982 | .324 | .301 |
| 5/8 — .6250 | .9375 | .922 | 1.083 | 1.051 | .387 | .363 |
| 3/4 — .7500 | 1.1250 | 1.088 | 1.299 | 1.240 | .446 | .398 |
| 7/8 — .8750 | 1.3125 | 1.269 | 1.516 | 1.447 | .510 | .458 |
| 1 — 1.0000 | 1.5000 | 1.450 | 1.732 | 1.653 | .575 | .519 |
| 1-1/8 — 1.1250 | 1.6875 | 1.631 | 1.949 | 1.859 | .639 | .579 |
| 1-1/4 — 1.2500 | 1.8750 | 1.812 | 2.165 | 2.066 | .751 | .687 |
| 1-3/8 — 1.3750 | 2.0625 | 1.994 | 2.382 | 2.273 | .815 | .747 |
| 1-1/2 — 1.5000 | 2.2500 | 2.175 | 2.598 | 2.480 | .880 | .808 |
| 1-3/4 — 1.7500 | 2.6250 | 2.538 | 3.031 | 2.893 | 1.009 | .929 |
| 2 — 2.0000 | 3.0000 | 2.900 | 3.464 | 3.306 | 1.138 | 1.050 |
| 2-1/4 — 2.2500 | 3.3750 | 3.262 | 3.897 | 3.719 | 1.251 | 1.155 |
| 2-1/2 — 2.5000 | 3.7500 | 3.625 | 4.330 | 4.133 | 1.505 | 1.401 |
| 2-3/4 — 2.7500 | 4.1250 | 3.988 | 4.763 | 4.546 | 1.634 | 1.522 |
| 3 — 3.0000 | 4.5000 | 4.350 | 5.196 | 4.959 | 1.763 | 1.643 |
Drawing notes: Optional chamfer 30° ± 2°; top chamfer approximately .016 in.
3. Material and Finish Codes
MS35691E defines five material and finish combinations used in the dash number system.
| Material | Finish |
|---|---|
| Steel, Carbon, Grade B | Cadmium Plate |
| Steel, Carbon, Grade C | Cadmium Plate |
| Steel, Carbon, Grade B | Phosphate Coated |
| CRES, 300 Series | Passivated 1/ |
| Brass | Black Oxide 2/ |
1/ See Requirement 5 2/ See Requirement 5
- CRES 300 Series: Passivated per ASTM A380. Maximum magnetic permeability 2.0 (air = 1.0) at field strength H = 200 Oersteds.
- Brass: Suitable for electrical and low-magnetic applications; black oxide or nickel plated.
4. Dash Number Matrix — Table II
The part numbers in Table II will only be used for design and engineering.
Group A — .2500-20UNC-2B / .2500-28UNF-2B / .3125-18UNC-2B / .3125-24UNF-2B
| Material | .2500-20UNC-2B | .2500-28UNF-2B | .3125-18UNC-2B | .3125-24UNF-2B |
|---|---|---|---|---|
| Steel, Carbon, Gr. B, Cadmium Plate | 1 | 5 | 9 | 13 |
| Steel, Carbon, Gr. C, Cadmium Plate | 2 | 6 | 10 | 14 |
| Steel, Carbon, Gr. B, Phosphate Coated | 406 | 426 | 506 | 526 |
| CRES, 300 Series, Passivated 1/ | 3 | 7 | 11 | 15 |
| Brass, Black Oxide 2/ | 4 | 8 | 12 | 16 |
Group B — .3750-16UNC-2B / .3750-24UNF-2B / .4375-14UNC-2B / .4375-20UNF-2B
| Material | .3750-16UNC-2B | .3750-24UNF-2B | .4375-14UNC-2B | .4375-20UNF-2B |
|---|---|---|---|---|
| Steel, Carbon, Gr. B, Cadmium Plate | 17 | 21 | 25 | 29 |
| Steel, Carbon, Gr. C, Cadmium Plate | 18 | 22 | 26 | 30 |
| Steel, Carbon, Gr. B, Phosphate Coated | 606 | 626 | 706 | 726 |
| CRES, 300 Series, Passivated 1/ | 19 | 23 | 27 | 31 |
| Brass, Black Oxide 2/ | 20 | 24 | 28 | 32 |
Group C — .5000-13UNC-2B / .5000-20UNF-2B / .5625-12UNC-2B / .5625-18UNF-2B
| Material | .5000-13UNC-2B | .5000-20UNF-2B | .5625-12UNC-2B | .5625-18UNF-2B |
|---|---|---|---|---|
| Steel, Carbon, Gr. B, Cadmium Plate | 33 | 37 | 41 | 45 |
| Steel, Carbon, Gr. C, Cadmium Plate | 34 | 38 | 42 | 46 |
| Steel, Carbon, Gr. B, Phosphate Coated | 806 | 826 | • | • |
| CRES, 300 Series, Passivated 1/ | 35 | 39 | 43 | 47 |
| Brass, Black Oxide 2/ | 36 | 40 | 44 | 48 |
Group D — .6250-11UNC-2B / .6250-18UNF-2B / .7500-10UNC-2B / .7500-16UNF-2B
| Material | .6250-11UNC-2B | .6250-18UNF-2B | .7500-10UNC-2B | .7500-16UNF-2B |
|---|---|---|---|---|
| Steel, Carbon, Gr. B, Cadmium Plate | 49 | 53 | 57 | 61 |
| Steel, Carbon, Gr. C, Cadmium Plate | 50 | 54 | 58 | 62 |
| Steel, Carbon, Gr. B, Phosphate Coated | 1006 | 1026 | 1206 | 1226 |
| CRES, 300 Series, Passivated 1/ | 51 | 55 | 59 | 63 |
| Brass, Black Oxide 2/ | 52 | 56 | 60 | 64 |
Group E — .8750-9UNC-2B / .8750-14UNF-2B / 1.0000-8UNC-2B / 1.0000-12UNF-2B
| Material | .8750-9UNC-2B | .8750-14UNF-2B | 1.0000-8UNC-2B | 1.0000-12UNF-2B |
|---|---|---|---|---|
| Steel, Carbon, Gr. B, Cadmium Plate | 65 | 69 | 73 | 77 |
| Steel, Carbon, Gr. C, Cadmium Plate | 66 | 70 | 74 | 78 |
| CRES, 300 Series, Passivated 1/ | 67 | 71 | 75 | 79 |
| Brass, Black Oxide 2/ | 68 | 72 | 76 | 80 |
Group F — 1.1250-7UNC-2B / 1.1250-12UNF-2B / 1.2500-7UNC-2B / 1.2500-12UNF-2B
| Material | 1.1250-7UNC-2B | 1.1250-12UNF-2B | 1.2500-7UNC-2B | 1.2500-12UNF-2B |
|---|---|---|---|---|
| Steel, Carbon, Gr. B, Cadmium Plate | 81 | 85 | 89 | 93 |
| Steel, Carbon, Gr. C, Cadmium Plate | 82 | 86 | 90 | 94 |
| CRES, 300 Series, Passivated 1/ | 83 | 87 | 91 | 95 |
| Brass, Black Oxide 2/ | 84 | 88 | 92 | 96 |
Group G — 1.3750-6UNC-2B / 1.3750-12UNF-2B / 1.5000-6UNC-2B / 1.5000-12UNF-2B
| Material | 1.3750-6UNC-2B | 1.3750-12UNF-2B | 1.5000-6UNC-2B | 1.5000-12UNF-2B |
|---|---|---|---|---|
| Steel, Carbon, Gr. B, Cadmium Plate | 97 | 101 | 105 | 109 |
| Steel, Carbon, Gr. C, Cadmium Plate | 98 | 102 | 106 | 110 |
| CRES, 300 Series, Passivated 1/ | 99 | 103 | 107 | 111 |
| Brass, Black Oxide 2/ | 100 | 104 | 108 | 112 |
Group H — 1.7500-5UNC-2B / 2.0000-4½UNC-2B / 2.2500-4½UNC-2B / 2.5000-4UNC-2B
| Material | 1.7500-5UNC-2B | 2.0000-4½UNC-2B | 2.2500-4½UNC-2B | 2.5000-4UNC-2B |
|---|---|---|---|---|
| Steel, Carbon, Gr. B, Cadmium Plate | 113 | 117 | 121 | 125 |
| Steel, Carbon, Gr. C, Cadmium Plate | 114 | 118 | 122 | 126 |
| CRES, 300 Series, Passivated 1/ | 115 | 119 | 123 | 127 |
| Brass, Black Oxide 2/ | 116 | 120 | 124 | 128 |
Group I — 2.7500-4UNC-2B / 3.0000-4UNC-2B
| Material | 2.7500-4UNC-2B | 3.0000-4UNC-2B |
|---|---|---|
| Steel, Carbon, Gr. B, Cadmium Plate | 129 | 133 |
| Steel, Carbon, Gr. C, Cadmium Plate | 130 | 134 |
| CRES, 300 Series, Passivated 1/ | 131 | 135 |
| Brass, Black Oxide 2/ | 132 | 136 |
5. Part Number Coding
The MS35691E part number is constructed as follows:
- Base number: MS35691
- Optional prefix: B (Black Oxide CRES) or N (Nickel Plated Brass)
- Dash number: Identifies thread size, material, and finish per Table II
Examples:
- MS35691-3 — .2500-20UNC-2B, CRES 300 Series, Passivated
- MS35691-35 — .5000-13UNC-2B, CRES 300 Series, Passivated
- MS35691-67 — .8750-9UNC-2B, CRES 300 Series, Passivated
6. Reference Documents
- MS35691E — Nut, Plain, Hexagon (Jam) UNC-2B and UNF-2B (23 March 2005)
- MS35691D — Superseded revision (29 August 1984)
- ASTM A380 — Standard Practice for Cleaning, Descaling, and Passivation of Stainless Steel Parts
- ASTM A153 — Standard Specification for Zinc Coating (Hot-Dip) on Iron and Steel Hardware
This article is provided for reference and informational purposes only. All dimensions and specifications are derived from MS35691E (Rev 23 March 2005). Always verify against the current revision of the applicable standard before procurement or use in design.