The ASTM A563 specification covers the chemical and mechanical requirements for carbon and alloy steel nuts used on bolts, studs, and externally threaded fasteners. The charts below address over tapping allowances for hot-dip galvanized nuts, grade marking requirements, and mechanical requirements. For information on suitable nuts for various grades of bolts, visit the  Nut Compatibility Chart.

According the A563 specification, “The requirements for any grade of nut may, at the supplier’s option, and with notice to the purchaser, be fulfilled by furnishing nuts of one of the stronger grades specified herein unless such a substitution is barred in the inquiry and purchase order”. This is important because some nut grades are not readily available in certain sizes and finishes. Additionally, the specification allows for the substitution of ASTM A194 grade 2H nuts in lieu of A563 grade DH nuts due to the lack of availability of grade DH nuts in nominal sizes 3/4″ and larger.

Hot-dip galvanized nuts must be tapped oversize to allow for the added thickness of the zinc on the threads of the externally threaded fastener. These allowances are addressed in the chart below and a more detailed explanation of this site.

Various nut styles exist and to some degree are determined by their grade. These styles include hex,  heavy hex,  square,  jam,  coupling, and  sleeve.


A563 Grades
A Carbon steel, hex or heavy hex
B Carbon steel, hex or heavy hex
C Carbon steel, quenched and tempered, heavy hex
D Carbon steel, quenched and tempered, heavy hex
DH Carbon steel, quenched and tempered, heavy hex
C3 Weathering steel, quenched and tempered, heavy hex
DH3 Weathering steel, quenched and tempered, heavy hex

A563 Mechanical Properties
Grade Style Size, in. Proof Load, ksi Hardness, HBN
Plain Galvanized
A Hex 1/4 - 1-1/2 90 68 116 - 302
Heavy Hex 1/4 - 4 100 75 116 - 302
B Heavy Hex 1/4 - 1 133 100 121 - 302
Heavy Hex 1-1/8 - 1-1/2 116 87 121 - 302
C / C3 Heavy Hex 1/4 - 4 144 144 143 - 352
D Heavy Hex 1/4 - 4 150 150 248 - 352
DH / DH3 Heavy Hex 1/4 - 4 175 150 248 - 352
For UNC, 8UN, 6UN, and Coarse Pitch Threads

A563 Chemical Properties
Element Grades O, A, B, C D** DH**
Carbon 0.55% max 0.55% max 0.20 - 0.55%
Manganese, min 0.30% 0.60%
Phosphorus, max 0.12% 0.04% 0.04%
Sulfur, max 0.15%* 0.05% 0.05%
* For grades O, A and B a sulfur content of 0.23% max is acceptable with the purchasers approval
** For grades D and DH a sulfur content of 0.05 - 0.15% is acceptable provided the manganese is 1.35% min
Element Classes for Grade C3* DH3
A B C D E F N
Carbon 0.33 - 0.40% 0.38 - 0.48% 0.15 - 0.25% 0.15 - 0.25% 0.20 - 0.25% 0.20 - 0.25% 0.20 - 0.53%
Manganese 0.90 - 1.20% 0.70 - 0.90% 0.80 - 1.35% 0.40 - 1.20% 0.60 - 1.00% 0.90 - 1.20% 0.40% min
Phosphorus 0.040% max 0.06 - 0.12% 0.035% max 0.040% max 0.040% max 0.040% max 0.07 - 0.15% 0.046% max
Sulfur, max 0.050% 0.050% 0.040% 0.050% 0.040% 0.040% 0.050% 0.050%
Silicon 0.15 - 0.35% 0.30 - 0.50% 0.15 - 0.35% 0.25 - 0.50% 0.15 - 0.35% 0.15 - 0.35% 0.20 - 0.90%
Copper 0.25 - 0.45% 0.20 - 0.40% 0.20 - 0.50% 0.30 - 0.50% 0.30 - 0.60% 0.20 - 0.40% 0.25 - 0.55% 0.20% min
Nickel 0.25 - 0.45% 0.50 - 0.80% 0.25 - 0.50% 0.50 - 0.80% 0.30 - 0.60% 0.20 - 0.40% 1.00% max 0.20% min**
Chromium 0.45 - 0.65% 0.50 - 0.75% 0.30 - 0.50% 0.50 - 1.00% 0.60 - 0.90% 0.45 - 0.65% 0.30 - 1.25% 0.45% min
Vanadium 0.020% min
Molybdenum 0.06% max 0.10% max 0.15% min**
Titanium 0.05% max
* Selection of a class shall be at the option of the manufacturer
** Nickel or Molybdenum may be used.

A563 Grade Identification Markings
Grade Identification Marking Specification Material Nominal Size, In. Proof Load Stress, ksi Hardness Rockwell See Note
Min Max
no_mark ASTM A563 Grade O Carbon Steel 1/4 - 1-1/2 69 B55 C32 2,3
ASTM A563 Grade A Carbon Steel 1/4 - 1-1/2 90 B68 C32 2,3
ASTM A563 Grade B Carbon Steel 1/4 - 1 120 B69 C32 2,3
>1 - 1-1/2 105
C ASTM A563 Grade C Carbon Steel, may be Quenched and Tempered 1/4 - 4 144 B78 C38 4
C3 ASTM A563 Grade C3 Atmospheric Corrosion Resistant Steel, may be Quenched and Tempered 1/4 - 4 144 B78 38 4,6
D ASTM A563 Grade D Carbon Steel, may be Quenched and Tempered 1/4 - 4 150 B84 C38 5
DH ASTM A563 Grade DH Carbon Steel, Quenched and Tempered 1/4 - 4 175 C24 C38 5
DH3 ASTM A563 Grade DH3 Atmospheric Corrosion Resistant Steel, Quenched and Tempered 1/4 - 4 175 C24 C38 4,6
NOTES:
  1. In addition to the indicated grade marking, all grades, except A563 grades O, A, and B, must be marked for manufacturer identification.
  2. Nuts are not required to be marked unless specified by the purchaser. When marked, the identification marking shall be the grade letter O, A, or B.
  3. Properties shown are those of nonplated or noncoated coarse thread nuts.
  4. Properties shown are those of coarse thread heavy hex nuts.
  5. Properties shown are those of coarse thread heavy hex nuts. Other nuts styles and fine threads may apply.
  6. The nut manufacturer, at his option, may add other markings to indicate the use of atmospheric corrosion resistant steel.
Inch Fastener Standards. 7th ed. Cleveland: Industrial Fasteners Institute, 2003. n-80-n-81.

For Nuts: Hot Dipped Galvanized per Specification A153, Cl.C

Thread Dimensions and Oversizing Allowances
Nominal Nut Size, in. and Pitch Diametral Allowance, in. Pitch Diameter
Min Max
0.250 - 20 0.016 0.2335 0.2384
0.312 - 18 0.017 0.2934 0.2987
0.375 - 16 0.017 0.3514 0.3571
0.437 - 14 0.018 0.4091 0.4152
0.500 - 13 0.018 0.4680 0.4745
0.0562 - 12 0.020 0.5284 0.5352
0.625 - 11 0.020 0.5860 0.5932
0.750 - 10 0.020 0.7050 0.7127
0.875 - 9 0.022 0.8248 0.8330
1.000 - 8 0.024 0.9428 0.9516
1.125 - 8 0.024 1.0678 1.0768
1.125 - 7 0.024 1.0562 1.0656
1.250 - 8 0.024 1.1928 1.2020
1.250 - 7 0.024 1.1812 1.1908
1.375 - 8 0.027 1.3208 1.3301
1.375 - 6 0.027 1.2937 1.3041
1.500 - 8 0.027 1.4458 1.4553
1.500 - 6 0.027 1.4187 1.4292
1.750 - 5 0.050 1.6701 1.6817
2.000 - 4.5 0.050 1.9057 1.9181
2.250 - 4.5 0.050 2.1557 2.1683
2.500 - 4 0.050 2.3876 2.4011
2.750 - 4 0.050 2.6376 2.6513
3.000 - 4 0.050 2.8876 2.9015
3.250 - 4 0.050 3.1376 3.1517
3.500 - 4 0.050 3.3876 3.4019
3.750 - 4 0.050 3.6376 3.6521
4.000 - 4 0.050 3.8876 3.9023
Inch Fastener Standards. 7th ed. Cleveland: Industrial Fasteners Institute, 2003. B-173.