Grade markings, tensile and yield minimums and hardness limits for ASTM A193, A320 and A453 studs and bolts and ASTM A194 heavy hex nuts. The printable PDF sheet is at the bottom of the page. Values are for reference; confirm against the current edition of the governing standard. Send us your print for a quote or call (281) 581-0176.
Related: Torque Reference Charts · All technical docs
Bolting Grades and Markings
- Values are specification minimums (tensile, yield) and maximums (hardness) for the bolting material. Always confirm against the edition of the standard cited on the purchase order.
- Studs are marked on one end with the grade symbol and the manufacturer’s identification mark. Marking requirements, including size limits, are set by each specification.
- Class 2 strain-hardened stainless grades carry their own marking; the class must be stated on the order. Strength drops with diameter as shown.
- A320 impact tests: 20 ft-lbf average and 15 ft-lbf minimum single value for L7, L43 and L7M at the listed test temperature.
Stud and Bolt Grades
| Specification and Grade | Material | Diameter (in.) | Tensile Min. (ksi) | Yield Min. (ksi) | Hardness Max. | Stud End Marking | Typical Use |
|---|---|---|---|---|---|---|---|
| ASTM A193 — HIGH-TEMPERATURE OR HIGH-PRESSURE SERVICE | |||||||
| B7 | Cr-Mo alloy steel, Q&T | 2-1/2 and under | 125 | 105 | 321 HBW / 35 HRC | B7 | General flange bolting |
| Over 2-1/2 to 4 | 115 | 95 | 321 HBW / 35 HRC | B7 | |||
| Over 4 to 7 | 100 | 75 | 321 HBW / 35 HRC | B7 | |||
| B7M | Cr-Mo alloy steel, Q&T, hardness limited | 4 and under | 100 | 80 | 235 HBW / 99 HRB | B7M | Sour service (NACE) |
| Over 4 to 7 | 100 | 75 | 235 HBW / 99 HRB | B7M | |||
| B16 | Cr-Mo-V alloy steel, Q&T | 2-1/2 and under | 125 | 105 | 321 HBW / 35 HRC | B16 | Elevated temperature |
| Over 2-1/2 to 4 | 110 | 95 | 321 HBW / 35 HRC | B16 | |||
| Over 4 to 8 | 100 | 85 | 321 HBW / 35 HRC | B16 | |||
| B8 Cl. 1 | 304 stainless, carbide solution treated | All | 75 | 30 | 223 HBW | B8 | Corrosion, cryogenic |
| B8M Cl. 1 | 316 stainless, carbide solution treated | All | 75 | 30 | 223 HBW | B8M | Corrosion, cryogenic |
| B8 Cl. 2 | 304 stainless, solution treated and strain hardened | 3/4 and under | 125 | 100 | 321 HBW / 35 HRC | See note 3 | Higher-strength stainless |
| Over 3/4 to 1 | 115 | 80 | |||||
| Over 1 to 1-1/4 | 105 | 65 | |||||
| Over 1-1/4 to 1-1/2 | 100 | 50 | |||||
| B8M Cl. 2 | 316 stainless, solution treated and strain hardened | 3/4 and under | 110 | 95 | 321 HBW / 35 HRC | See note 3 | Higher-strength stainless |
| Over 3/4 to 1 | 100 | 80 | |||||
| Over 1 to 1-1/4 | 95 | 65 | |||||
| Over 1-1/4 to 1-1/2 | 90 | 50 | |||||
| ASTM A320 — LOW-TEMPERATURE SERVICE (CHARPY IMPACT TESTED) | |||||||
| L7 | Cr-Mo alloy steel, Q&T | 2-1/2 and under | 125 | 105 | 321 HBW / 35 HRC | L7 | Impact tested at −150°F |
| L7M | Cr-Mo alloy steel, hardness limited | 2-1/2 and under | 100 | 80 | 235 HBW / 99 HRB | L7M | −100°F; sour service |
| L43 | Ni-Cr-Mo alloy steel, Q&T | 4 and under | 125 | 105 | 321 HBW / 35 HRC | L43 | Impact tested at −150°F |
| ASTM A453 — HIGH-TEMPERATURE, AUSTENITIC (PRECIPITATION HARDENED) | |||||||
| 660 A, B, C | Iron-base superalloy (A-286 type) | All | 130 | 85 | 248–341 HB range | 660 + class | High temperature, high strength |
ASTM A194 Heavy Hex Nut Grades
| Grade | Material | Proof Load Stress (ksi) | Hardness | Nut Marking | Commonly Paired With |
|---|---|---|---|---|---|
| 2H | Carbon steel, Q&T | 175 | To 1-1/2: 248–327 HB (24–35 HRC) | 2H | A193 B7, B16; A320 L7 (when impact testing is not required) |
| 2HM | Carbon steel, Q&T, hardness limited | 150 | 159–237 HB (84–99 HRB) | 2HM | A193 B7M; sour service |
| 4 | Carbon-molybdenum steel, Q&T | 175 | 248–327 HB (24–35 HRC) | 4 | A193 B16, B7; elevated temperature |
| 7 | Alloy steel (Cr-Mo), Q&T | 175 | 248–327 HB (24–35 HRC) | 7 | A193 B7, B16; A320 L7 / L43 (with impact testing as specified) |
| 7M | Alloy steel, Q&T, hardness limited | 150 | 159–237 HB (84–99 HRB) | 7M | A193 B7M; A320 L7M; sour service |
| 8 | 304 stainless | 80 | 126–300 HB | 8 | A193 B8 |
| 8M | 316 stainless | 80 | 126–300 HB | 8M | A193 B8M |
Nut notes:
- Nuts are heavy hex per ASME B18.2.2 unless specified. Values shown are for nuts with UNC or 8UN threads.
- Hardness and proof load ranges vary with nut size and thread series for some grades; check A194 for nuts larger than 1-1/2 in.
- Nuts are marked on one face with the grade symbol and the manufacturer’s identification mark.
- Pairings are common practice only. The governing piping or equipment code and the purchaser’s specification determine the required nut grade.
Ordering checklist:
- Specification, grade and class (for example, ASTM A193 Grade B8M Class 2).
- Supplementary requirements, such as impact testing for low-temperature service or NACE MR0175 hardness limits.
- Coating or finish (see sheet PB-TD-208) and certification: mill test reports with heat numbers, plus a certificate of conformance.
References: ASTM A193 · ASTM A320 · ASTM A453 · ASTM A194
- Reference only. Verify against the current edition of ASTM A193, A320, A453 and A194 and the joint owner’s procedure before use. Printable sheet: PB-TD-204.
About the Bolting Grades and Markings chart
This sheet lists the common stud, bolt and nut grades used in flange bolting: ASTM A193, A320 and A453 for studs and bolts, and A194 for heavy hex nuts. For each grade it gives material, diameter range, minimum tensile and yield strength, maximum hardness, stud end marking and typical use.
How to read the chart
- Specification and grade: For example A193 B7. The grade you order.
- Diameter: Size band. Strength minimums change with diameter.
- Tensile and yield: Minimum strength, ksi. For example B7 through 2-1/2 inch is 125 tensile and 105 yield.
- Hardness max: Brinell or Rockwell. For example B7M is limited to 235 HBW for sour service.
- Marking: Stud end stamp. Grade symbol plus the maker’s identification mark.
Ordering from Patriot Bolt
Patriot Bolt manufactures stud bolts, heavy hex nuts and special flange bolting from certified round bar in B7, B7M, L7, B16, stainless and nickel grades, with coatings on request. Mill test reports come with every order.
Common questions
What impact test applies to A320 grades?
L7, L43 and L7M require 20 ft-lbf average and 15 ft-lbf minimum single value at the listed test temperature.
Do Class 2 stainless studs need a special marking?
Yes. Strain-hardened Class 2 grades carry their own marking, and the class must be stated on the order.
See also: Stud Bolts · Sour Service Bolting · Fastener Materials Matrix · Request a quote