Scope
ASTM F594 covers stainless steel nuts in inch-series from 1/4" through 1-1/2", grouped by alloy family to match F593 bolts. Hex and heavy hex styles are standard; jam, flange, and other patterns are available.
Alloy groups
F594 uses the same group numbering as F593:
| Group | Alloy family | Common AISI/UNS | Typical use |
|---|---|---|---|
| Group 1 | Austenitic | 304, 305 | Standard stainless; general corrosion resistance |
| Group 2 | Austenitic | 316 | Marine, chloride-bearing, chemical |
| Group 3 | Austenitic | 321, 347 | Stabilized for welding and moderate high temp |
| Group 4 | Ferritic | 430 | Moderate service, magnetic |
| Group 5 | Martensitic | 410, 416, 431 | Higher strength, magnetic |
| Group 6 | Precipitation-hardened | 17-4 PH | High strength + corrosion |
Conditions
Condition designation parallels F593:
- Condition A — solution annealed; the default
- Condition CW — cold worked, higher proof load
- Condition SH — strain hardened, highest proof load for austenitic grades
- Condition H / HT — for martensitic and precipitation-hardening grades
Mechanical properties — Groups 1 and 2 (austenitic)
F594 nuts are acceptance-tested by proof load (the force the nut can withstand without stripping):
Condition A
| Size range | Proof Load Stress |
|---|---|
| 1/4" through 1-1/2" | 80 ksi |
Condition CW
| Size range | Proof Load Stress |
|---|---|
| 1/4" through 5/8" | 100 ksi |
| Over 5/8" through 3/4" | 85 ksi |
Condition SH
| Size range | Proof Load Stress |
|---|---|
| 1/4" through 5/8" | 120 ksi |
| Over 5/8" through 3/4" | 110 ksi |
| Over 3/4" through 1-1/2" | 100 ksi |
The nut proof load is set above the bolt tensile capacity so the bolt, not the nut, governs failure. This is the same design principle as A194 and A563.
Match the group — don't mix
The single most important rule for stainless fastener selection: the bolt and nut should be the same alloy group. Mixing puts the corrosion resistance of the assembly at the level of the weaker material, defeats the reason stainless was specified in the first place, and can create galvanic couples in wet service.
The practical exception: specifying Nitronic 60 (galling-resistant austenitic stainless) nuts on 316 bolts in service where galling is chronic. Nitronic 60 is compositionally similar enough to 316 that galvanic mismatch is negligible, and the galling resistance solves the bigger problem.
Galling with stainless nuts — same story
Austenitic stainless threads cold-weld to each other under pressure, especially during fast installation. A stainless nut will gall against a stainless bolt under nearly identical conditions to any other stainless-stainless thread contact. Mitigation:
- Use an anti-seize lubricant (nickel-based or molybdenum disulfide)
- Reduce tool speed; slower installation = less frictional heat
- For chronic issues, specify Nitronic 60 nuts or bolts (or both)
Recommended pairing
| F594 nut | Typical bolt | Typical washer |
|---|---|---|
| Group 1 (304) | F593 Group 1 | Stainless 304 or plain F844 |
| Group 2 (316) | F593 Group 2 | Stainless 316 preferred |
| Group 6 (17-4 PH) | F593 Group 6 | Stainless, matching |
For assemblies that will be immersed or continuously wet, use a stainless washer of the same group. Mixing a carbon-steel washer under a stainless nut in wet service causes galvanic corrosion of the washer and rust streaks on the stainless parts.
Applications
- Marine hardware (316)
- Exterior architectural (316)
- Food, beverage, pharmaceutical (304 or 316 depending on washdown chemistry)
- Swimming pool and spa hardware (316)
- Chemical equipment (316 for chloride, 321/347 for elevated-temp chloride-light)
- Outdoor infrastructure where the bolt is stainless
Marking
- Group identification mark (1, 2, 3, etc.) on one face
- Manufacturer's identification symbol
- Common practice: "18-8" stamp for Group 1, "316" stamp for Group 2
Related specifications
- F593 — Stainless bolts (always pair within group)
- F836M — Metric stainless nuts
- A193 / A194 Grade 8, 8M — Stainless bolting/nuts for pressure and temperature service
- F844 — Plain flat washers (acceptable in dry service)
Documentation
California Fastener F594 orders ship with mill certificates showing alloy group, condition, heat number, chemistry, and proof-load test results. Dual-certified material (304/304L or 316/316L) is identified on the cert.