A4 Stainless Steel Imperial Hex Nuts (UNC / UNF) combine the dimensional form of ANSI/ASME B18.2.2 / BS 1768 with the material properties of grade ISO 3506 group A4 (316 / 1.4401), commonly supplied A4-80: superior, including marine and chloride environments, largely non-magnetic, service range approx. -200 °C to +400 °C, subject to the property class and the joint. This page summarizes the grade data, its corrosion behavior in service, the comparable grades, and the sizes supplied.
Why Choose A4 Stainless Steel for Imperial Hex Nuts (UNC / UNF)
Specified for marine, coastal and chemical applications. For imperial hex nuts (unc / unf), this matters when superior, including marine and chloride environments is the primary requirement.
Mechanical & Physical Properties
| Grade designation | ISO 3506 group A4 (316 / 1.4401), commonly supplied A4-80 |
|---|---|
| Magnetic response | Largely non-magnetic |
| Service temperature | approx. -200 °C to +400 °C, subject to the property class and the joint |
| Corrosion characteristic | Superior, including marine and chloride environments |
Galvanic & Galling Considerations
Two important notes for stainless imperial hex nuts (unc / unf): (1) stainless can gall on stainless threads under load — use a thread lubricant or anti-galling compound, especially for M6 and below; (2) when joined to aluminum or galvanized steel, stainless can drive galvanic corrosion of the less-noble metal in wet service — isolate with a coating or sleeve where appropriate.
Comparable Grades
For Imperial Hex Nuts (UNC / UNF), the alternative stainless grade is A2 (304). The practical dividing line is chlorides: A2 (304) is fine until salt is involved, and A4 (316) exists for the cases where it is — coastal, marine and road-salt service. Neither reaches the strength of a plated class 8.8 or 10.9 fastener.
Using Stainless Fasteners in Aluminum
Expect the aluminum to corrode, not the fastener — stainless sits higher in the galvanic series, so the aluminum is the one that gives up material. A small fastener in a thick section spreads the loss over a large area and is usually fine; a large fastener in thin sheet concentrates it and is not. Keep water out of the joint, or isolate the two metals with a nylon or coated washer and a sealant.
Sizes of Imperial Hex Nuts (UNC / UNF) Available in A4 Stainless 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 A4 Stainless Steel.
Custom manufacturing · Made to drawing
Need this nut in a grade that is not listed?
A4 Stainless Steel is one of the grades the catalog describes. Thread, height, across-flats, property class, locking feature and flange form can all be varied, including thread sizes the standard series does not run to. Made by cold heading or tapping.
Minimum order from 2,000 pieces; samples within 7 days of drawing approval.
