ASTM A194 Nut Grades — Overview and Selection
ASTM A194 covers carbon and alloy steel nuts for high-pressure and high-temperature service — grades 2H, 2HM, 4, 7, 7M, 8 and 8M in heavy hex, square and heavy hex structural patterns. A selection map by stud pairing: B7→2H, B7M→2HM (sour service), B8→8, B8M→8M (chloride/marine), A320 L7→4 or 7 (low temperature).
Last updated: 2026-11
Specifications
ASTM A194 is the standard specification for carbon and alloy steel nuts (with stainless grades 8 and 8M) for bolts in high-pressure or high-temperature service — the scope covers heavy hex nuts, square nuts and heavy hex structural nuts. The specification splits into two families with opposite selection logic. The carbon/alloy family earns its place through heat treatment and strength: Grade 2H, the quenched-and-tempered medium-carbon workhorse rated at 175 ksi proof-load stress over 1/4"–4", is the default partner for A193 B7 studs in refinery and pipeline work; 2HM is the hardness-controlled variant for sour service; grades 4 and 7 serve low-temperature and high-strength alloy assemblies. The austenitic stainless family — Grade 8 (304 chemistry) and Grade 8M (316 chemistry with 2–3% molybdenum) — trades raw strength for corrosion resistance, solution treated rather than quenched and tempered. The fastest way to the right grade is to start from the stud: the collected pairing tables map every common A193/A320 stud to its matching nut grade.
| Standard | ASTM A194 — carbon and alloy steel nuts for high-pressure / high-temperature bolting; also covers austenitic stainless grades |
|---|---|
| Nut patterns in scope | Heavy hex nuts, square nuts, heavy hex structural nuts |
| Grades covered | 2H, 2HM, 4, 7, 7M (carbon/alloy); 8, 8M (austenitic stainless) |
| General HP/HT flanges | A193 B7 studs + A194 2H nuts — the default refinery/pipeline pairing; 2H: 175 ksi proof load, C24–C38, 1/4"–4" |
| Sour service (NACE) | A193 B7M studs + A194 2HM nuts — controlled hardness |
| Corrosion / moderate temp | A193 B8 Class 1 studs + A194 8 nuts (304 chemistry) |
| Chloride / marine | A193 B8M Class 1 studs + A194 8M nuts (316 chemistry, Mo-bearing); 8M: 550 MPa min proof load, 126–321 HBW |
| Cryogenic / low temp | A320 L7 studs + A194 4 or 7 nuts |
Materials
- Medium-carbon steel (2H)
- Alloy steel (4, 7, 7M, 2HM)
- Austenitic stainless steel (8, 8M)
Ordering & documentation
Documents
Shipments are backed by Mill Test Certificate (MTC), Dimensional Report, Salt Spray Test Report on request, with full batch traceability from raw material to finished product. Quality management follows the owner-confirmed compliance list: ISO 9001:2015, RoHS, REACH. Exact document sets are confirmed on the order.
Quotation
- The fastener family (ASTM A194 Nut Grades — Overview and Selection) plus the standard designation from your drawing — DIN / ISO / JIS / ASTM / ANSI, or a drawing for custom parts.
- Size (diameter and length), thread type (metric or inch), property class or grade, and coating or finish.
- Quantity per size and your target delivery date.
- Destination country, and any required documents (for example a mill test certificate) so the quote includes them.
Sample & supply
Minimum order quantity is 10,000 pieces. Stock items run 3–7 days. Quantities or variants outside the standard range are confirmed at quotation.
Storage & shipping
Parts are packed for export and shipped factory-direct to buyers in Europe, Asia, the Americas and the Middle East. Store fasteners dry and protected until installation, and keep coated parts in their packaging until use; specific packing and preservation requirements can be stated on the order and confirmed at quotation.
Frequently asked questions
How do I choose between ASTM A194 grades for a stud-bolt assembly?
Start from the stud, not the nut. The collected pairing tables map each stud specification to its matching nut grade: A193 B7 pairs with 2H for general high-temperature/high-pressure flanges, B7M pairs with 2HM for sour (NACE) service, B8 pairs with 8 and B8M with 8M for corrosion and chloride/marine service respectively, and A320 L7 studs take 4 or 7 nuts for cryogenic and low-temperature service. Match the nut grade to the stud specification of record — a stronger nut under a soft stud (or the reverse) shifts the failure point of the joint.
Which ASTM A194 grades are stainless steel?
Grades 8 and 8M — the austenitic stainless members of the specification. Grade 8 follows the 304 chemistry; Grade 8M adds 2.00–3.00% molybdenum (316 chemistry) for pitting and crevice resistance in chloride service, with 550 MPa minimum proof-load stress and a 126–321 HBW band in Class 1. Both are carbide solution treated rather than quenched and tempered. The remaining grades (2H, 2HM, 4, 7, 7M) are carbon or alloy steel.
What is the MOQ and lead time for this nut type?
The minimum order quantity is 10,000 pieces. Stock items ship in 3–7 days; non-stock items are confirmed at quotation. Common diameters in this nut type are widely stocked; confirm the exact schedule against quantity and size mix at quotation.
What should an RFQ for this nut type state?
State the standard designation (for example DIN 985 or DIN 6923), nominal thread size and pitch (metric coarse unless fine pitch is required), material and strength pairing with the mating bolt, finish (plain, zinc, or hot-dip galvanized where compatible), required certificates such as a mill test report per EN 10204 3.1, and quantity per size — plus destination country.
Request a Quote
Get factory-direct pricing from the manufacturer.
What to include in your inquiry
- ✓ Standard and property class (e.g. DIN 912, ISO 4762, class 8.8) — or a drawing for custom parts.
- ✓ Sizes, lengths and thread type (metric or inch).
- ✓ Quantity per size and your target delivery date.
- ✓ Destination country, plus any coating or finish requirement.
- ✓ Any documents you need with the shipment (e.g. mill test certificate) so the quote includes them.
- ✓ Your inquiry goes straight to the factory team by email and gets a reply within 24 hours.
- ✓ Factory-direct pricing
- ✓ Standard and custom specifications
- ✓ Factory-direct export to buyers in Europe, Asia, the Americas and the Middle East
- ✓ Full fastener family support