Patriot Bolt machines ASTM A194 Grade 3 heavy hex nuts from Type 501 steel (UNS S50100), the same 5 percent chromium, 1/2 percent molybdenum steel used in A193 B5 studs. Grade 3 nuts are quenched and tempered at 1050 °F minimum.
We make Grade 3 nuts alone or with matching B5 studs. Nuts machined from bar are marked 3B, as the specification requires. Every order ships with mill test reports traceable to the heat.
A194 Grade 3 Heavy Hex Nuts at a Glance
- Specification
- ASTM A194 / ASME SA194 Grade 3
- Material
- Type 501, 5Cr-1/2Mo steel (UNS S50100)
- Heat treatment
- Quenched and tempered at 1050 °F min
- Proof stress
- 175 ksi heavy hex, 150 ksi hex
- Hardness
- 248–327 HBW / 24–35 HRC
- Matching stud
- A193 B5
Why Engineers Specify A194 Grade 3 Nuts
- Same alloy as B5. Stud and nut share 5Cr-1/2Mo chemistry, so both resist hot sulfur-bearing streams the same way.
- Full strength. A 175 ksi proof stress for heavy hex nuts, the same as 2H and Grade 7.
- Heat treated. Quenching and tempering at 1050 °F minimum give a consistent hardness window from nut to nut.
Grade 3 is an uncommon grade. Where a B5 joint is specified, ordering the studs and nuts together keeps the set matched.
A194 Grade 3 Specifications
A194 sets one proof stress and hardness range for Grade 3 heavy hex nuts.
| Nut style | Proof stress | Hardness, min | Hardness, max |
|---|---|---|---|
| Heavy hex, all sizes | 175 ksi | 248 HBW / 24 HRC | 327 HBW / 35 HRC |
| Hex, all sizes | 150 ksi | 248 HBW / 24 HRC | 327 HBW / 35 HRC |
A194 Grade 3 Chemical Composition
| Element | Weight % |
|---|---|
| Carbon | 0.10 min |
| Manganese | 1.00 max |
| Phosphorus | 0.040 max |
| Sulfur | 0.030 max |
| Silicon | 1.00 max |
| Chromium | 4.0–6.0 |
| Molybdenum | 0.40–0.65 |
Limits per the current edition of the specification. The mill test report for your heat is the controlling document.
Nut Styles
- Heavy hex nuts to ASME B18.2.2, the standard style for flange and structural studs.
- Heavy hex jam nuts where a thinner nut is needed.
- Threads: UNC through 1 in and 8UN above 1 in, or the thread on your drawing.
Applications and Industries
- Refining: Flanges on 5Cr-1/2Mo (P5 and F5) piping in hot, sulfur-bearing service. See Petrochemical & Refining.
- Heater and furnace piping: Hot hydrocarbon lines where B5 studs are specified.
- Power generation: Elevated-temperature joints that call for a 5Cr-Mo bolting set. See Power Generation.
Certification and Traceability
Patriot Bolt is ISO 9001:2015 certified. Each Grade 3 order includes mill test reports traceable to the heat, along with a certificate of conformance to the specification on your purchase order.
Nuts are marked 3, or 3B when machined from bar, with our identification on one face.
Compare Grade 3 with other bolting grades in our Fastener Materials Matrix.
A194 Grade 3 Heavy Hex Nuts FAQ
Which stud goes with A194 Grade 3 nuts?
ASTM A193 Grade B5. Both are made from 5Cr-1/2Mo Type 501 steel.
Is Grade 3 as strong as 2H?
Yes. Grade 3 heavy hex nuts carry the same 175 ksi proof stress as 2H and Grade 7. The difference is the 5 percent chromium content.
What does 3B mean on a nut?
The grade is the same. A194 adds the letter B when the nut is machined from bar stock instead of being forged.
Do you make matching B5 studs?
Yes. We machine A193 B5 stud bolts, so the stud and nuts can come from one source.
Request a Quote
Send us the alloy, nut style, thread size, specification and quantity, or upload your drawing. Our team will confirm the material and lead time. Call (281) 581-0176 or request a quote.
Related: B5 stud bolts · A193 B5 fasteners hub · A194 Grade 7 nuts · All nuts