Property Class 8.8 Steel (ISO 898-1 property class 8.8) is the workhorse medium-carbon alloy class for structural joints. When hex coupling nuts, unc are specified in this grade, the dimensions remain per ASME B18.2.2; the material determines corrosion behavior (requires plating (zinc) for corrosion protection) and the service temperature range (commonly limited to approx. +300 °C; confirm against the coating and the load). Both are covered below with the size table.
Why Choose Property Class 8.8 Steel for Hex Coupling Nuts, UNC
The workhorse medium-carbon alloy class for structural joints. For hex coupling nuts, unc, this matters when requires plating (zinc) for corrosion protection is the primary requirement.
Mechanical & Physical Properties
| Grade designation | ISO 898-1 property class 8.8 |
|---|---|
| Magnetic response | Magnetic |
| Service temperature | commonly limited to approx. +300 °C; confirm against the coating and the load |
| Corrosion characteristic | Requires plating (zinc) for corrosion protection |
Galvanic & Galling Considerations
For hex coupling nuts, unc in steel, the dominant compatibility issue is hydrogen embrittlement at high property classes (10.9 and above) when electroplated. Plating must be followed by an appropriate baking treatment, or a non-electroplated finish (mechanical zinc, zinc flake) should be substituted.
Comparable Grades
For Hex Coupling Nuts, UNC, class 10.9 or 12.9 is the comparable strength step. Move up when the joint preload approaches the proof load of the current class; move down when the joint is over-specified. For corrosion-critical service, switch to stainless A2 or A4.
Sizes of Hex Coupling Nuts, UNC Available in Property Class 8.8 Steel
| Size | Threads per inch | Width across flats s (in) | Nut height m (in) | Reference standard |
|---|---|---|---|---|
| #6 | 32 | 0.312 | 0.5 | ASME B18.2.2 |
| #8 | 32 | 0.312 | 0.625 | ASME B18.2.2 |
| #10 | 24 | 0.312 | 0.75 | ASME B18.2.2 |
| 1/4" | 20 | 0.438 | 1.75 | ASME B18.2.2 |
| 5/16" | 18 | 0.5 | 1.75 | ASME B18.2.2 |
| 3/8" | 16 | 0.562 | 1.75 | ASME B18.2.2 |
| 7/16" | 14 | 0.625 | 1.75 | ASME B18.2.2 |
| 1/2" | 13 | 0.688 | 1.75 | ASME B18.2.2 |
| 9/16" | 12 | 0.812 | 2.125 | ASME B18.2.2 |
| 5/8" | 11 | 0.812 | 2.125 | ASME B18.2.2 |
| 3/4" | 10 | 1 | 2.25 | ASME B18.2.2 |
| 7/8" | 9 | 1.25 | 2.5 | ASME B18.2.2 |
| 1" | 8 | 1.375 | 2.75 | ASME B18.2.2 |
| 1 1/8" | 7 | 1.5 | 3 | ASME B18.2.2 |
| 1 1/4" | 7 | 1.625 | 3 | ASME B18.2.2 |
| 1 1/2" | 6 | 2 | 3.5 | ASME B18.2.2 |
| 1 5/8" | 5.5 | 2.562 | 4.875 | ASME B18.2.2 |
| 1 3/4" | 5 | 2.75 | 5.25 | ASME B18.2.2 |
| 1 7/8" | 5 | 2.938 | 5.625 | ASME B18.2.2 |
| 2" | 4.5 | 3.125 | 6 | ASME B18.2.2 |
| 2 1/4" | 4.5 | 3.5 | 6.75 | ASME B18.2.2 |
| 2 1/2" | 4 | 3.875 | 7.5 | ASME B18.2.2 |
| 2 3/4" | 4 | 4.25 | 8.25 | ASME B18.2.2 |
| 3" | 4 | 4.625 | 9 | ASME B18.2.2 |
| 3 1/4" | 4 | 5 | 9.75 | ASME B18.2.2 |
| 3 1/2" | 4 | 5.375 | 10.5 | ASME B18.2.2 |
| 3 3/4" | 4 | 5.75 | 11.26 | ASME B18.2.2 |
| 4" | 4 | 6.125 | 12 | ASME B18.2.2 |
| 4 1/4" | 4 | 6.5 | 12.75 | ASME B18.2.2 |
| 4 1/2" | 4 | 6.875 | 13.5 | ASME B18.2.2 |
Dimensions are independent of the material: every size above is available in Property Class 8.8 Steel.
Custom manufacturing · Made to drawing
Need this nut in a grade that is not listed?
Grade 8 8 Steel is one of the grades the catalog describes. Thread size is the obvious variable and rarely the interesting one — height for clearance, across-flats for the tool already in the cell, and the locking feature for the vibration actually present. Made by cold heading or tapping.
Minimum order from 2,000 pieces; samples within 7 days of drawing approval.
