Property Class 12.9 Steel (ISO 898-1 property class 12.9) is the highest common strength class, for high-load machine assembly. When imperial hex nuts (unc / unf) are specified in this grade, the dimensions remain per ANSI/ASME B18.2.2 / BS 1768; the material determines corrosion behavior (requires plating or black-oxide 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 12.9 Steel for Imperial Hex Nuts (UNC / UNF)
The highest common strength class, for high-load machine assembly. For imperial hex nuts (unc / unf), this matters when requires plating or black-oxide protection is the primary requirement.
Mechanical & Physical Properties
| Grade designation | ISO 898-1 property class 12.9 |
|---|---|
| Magnetic response | Magnetic |
| Service temperature | commonly limited to approx. +300 °C; confirm against the coating and the load |
| Corrosion characteristic | Requires plating or black-oxide protection |
Galvanic & Galling Considerations
For imperial hex nuts (unc / unf) 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 Imperial Hex Nuts (UNC / UNF), class 8.8 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 Imperial Hex Nuts (UNC / UNF) Available in Property Class 12.9 Steel
| Nominal size | Thread series | Material options | Finish options |
|---|---|---|---|
| 1/4 in | UNC or UNF | carbon steel or A2/A4 stainless | black oxide / blue-white zinc / yellow zinc / hot-dip galvanized |
| 5/16 in | UNC or UNF | carbon steel or A2/A4 stainless | black oxide / blue-white zinc / yellow zinc / hot-dip galvanized |
| 3/8 in | UNC or UNF | carbon steel or A2/A4 stainless | black oxide / blue-white zinc / yellow zinc / hot-dip galvanized |
| 1/2 in | UNC or UNF | carbon steel or A2/A4 stainless | black oxide / blue-white zinc / yellow zinc / hot-dip galvanized |
| 5/8 in | UNC or UNF | carbon steel or A2/A4 stainless | black oxide / blue-white zinc / hot-dip galvanized |
| 3/4 in | UNC or UNF | carbon steel or A2/A4 stainless | black oxide / blue-white zinc / hot-dip galvanized |
Dimensions are independent of the material: every size above is available in Property Class 12.9 Steel.
Custom manufacturing · Made to drawing
Need this nut in a grade that is not listed?
Grade 12 9 Steel is one of the grades the catalog describes. Height and across-flats are the two most often changed — a thinner nut for clearance, a larger hex for a tool that is already on the line. Made by cold heading or tapping.
Minimum order from 2,000 pieces; samples within 7 days of drawing approval.
