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ASTM A563
The ASTM A563 specification covers the chemical and mechanical requirements for carbon and alloy steel nuts used on bolts, studs, and externally threaded fasteners.
ASTM A563
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 ¾"" 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 issue can be found in the Frequently Asked Questions section 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.
Scope
Standard specification for carbon and alloy steel nuts.
Grades
A
Low carbon steel, hex or heavy hex
B
Low 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
Mechanical Properties
Grade
Style
Size, in.
Proof Load, ksi
Hardness, HBN
Black
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
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
ASTM A563 Grade C
Carbon Steel, may be Quenched and Tempered
1/4 - 4
144
B78
C38
4
ASTM A563 Grade C3
Atmospheric Corrosion Resistant Steel, may be Quenched and Tempered
1/4 - 4
144
B78
38
4,6
ASTM A563 Grade D
Carbon Steel, may be Quenched and Tempered
1/4 - 4
150
B84
C38
5
ASTM A563 Grade DH
Carbon Steel, Quenched and Tempered
1/4 - 4
175
C24
C38
5
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.
Thread Dimensions and Oversizing Allowances
for Nuts: Hot Dipped Galvanized per Specification A153, C1.C
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.
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