Coupling Nut Grades
When selecting coupling nut grades, it is important to ensure the coupling nut can fully develop the strength of the threaded fasteners it joins. Accordingly, coupling nuts are graded in the same manner as standard hex nuts. As a result, they must meet specific ASTM and SAE chemical and mechanical requirements in order to remain compatible with the various grades of fasteners they are used with. In addition, the dimensional requirements for coupling nuts are governed by ASME B18.2.2, Which Specifies Various grades of fasteners that they are used with. Dimensional requirements are covered under ASME B18.2.2
Nut Compatibility Chart by grade
The chart below identifies the appropriate grades of coupling nuts to be used with corresponding grades of bolts, threaded rods, and other fasteners. Understanding coupling nut grades is critical to ensuring proper strength, compatibility, and performance in an assembled fastener system. In some applications, stainless steel coupling nut grades are specified by raw material classification—such as Type 304 or Type 316—rather than by an ASTM nut grade specification.
| Grade of Bolt | Surface Finish | Nominal Size Inches | A563 Grade and ANSI Nut Style | |||
|---|---|---|---|---|---|---|
| Recommended | Suitable | |||||
| Hex | Heavy Hex |
Hex | Heavy Hex |
|||
|
A307 Grade A & C
|
Any | 1⁄4 to 11⁄2 |
A
|
B,D,DH
|
A,B,C,D,DH,DH3
|
|
| >11⁄2 to 2 |
A
|
A
|
C,D,DH,DH3
|
|||
| >2 to 4 |
A
|
C,D,DH,DH3
|
||||
|
A307 Grade B
|
Any | 1⁄4 to 11⁄2 |
A
|
B,D,DH
|
A,B,C,D,DH,DH3
|
|
| >11⁄2 to 2 |
A
|
A
|
||||
| >2 to 4 |
A
|
|||||
|
F3125 A325 Type 1
|
Plain | 1⁄2 – 11⁄2 |
C
|
C3,D,DH,DH3
|
||
| Galvanized | 1⁄2 – 11⁄2 |
DH
|
||||
|
F3125 A325 Type 3
|
Plain | 1⁄2 – 11⁄2 |
C3
|
DH3
|
||
|
A354 Grade BC
|
Plain | 1⁄4 to 11⁄2 |
C
|
D,DH
|
C3,D,DH,DH3
|
|
| >11⁄2 to 4 |
C
|
C3,D,DH,DH3
|
||||
| Galvanized | 1⁄4 to 11⁄2 |
DH
|
||||
| >11⁄2 to 4 |
DH
|
|||||
|
A354 Grade BD
|
Plain | 1⁄4 to 11⁄2 |
DH
|
DH
|
D,DH,DH3
|
|
| >11⁄2 to 4 |
DH
|
DH3
|
||||
|
A449
|
Plain | 1⁄4 to 11⁄2 |
B
|
D,DH
|
B,C,C3,D,DH,DH3
|
|
| >11⁄2 to 3 |
A
|
C,C3,D,DH,DH3
|
||||
| Galvanized | 1⁄4 to 11⁄2 |
DH
|
D,DH
|
D
|
||
| >11⁄2 to 3 |
DH
|
D
|
||||
|
F3125 A490 Type 1
|
Plain | 1⁄2 – 11⁄2 |
DH
|
DH3
|
||
|
F3125 A490 Type 3
|
Plain | 1⁄2 – 11⁄2 |
DH3
|
|||
|
A687
|
Plain | 5⁄8 – 3 |
D
|
DH,DH3
|
||
| Galvanized | 5⁄8 – 3 |
DH
|
||||
|
F1554 Grade 36
|
Any | 1⁄2 to 11⁄2 |
A
|
B,D,DH
|
A,B,C,D,DH,DH3
|
|
| >11⁄2 to 4 |
A
|
C,D,DH,DH3
|
||||
|
F1554 Grade 55
|
Plain | 1⁄2 to 11⁄2 |
A
|
B,D,DH
|
A,B,C,D,DH,DH3
|
|
| >11⁄2 to 4 |
A
|
C,D,DH,DH3
|
||||
| Galvanized | 1⁄2 to 4 |
A
|
C,D,DH,DH3
|
|||
|
F1554 Grade 105
|
Plain | 1⁄2 to 11⁄2 |
D
|
DH,DH3
|
||
| >11⁄2 to 3 |
DH
|
DH3
|
||||
| Galvanized | 1⁄2 to 3 |
DH
|
DH3
|
|||
| 1. Nuts made in accordance with the requirements of Specification A194 Grade 2H and marked with its grade symbol are an acceptable equivalent for Grade DH nuts. (per ASTM A563/A563M-21a, Table X1.1) | ||||||