Stud bolt & nut grades — B7, B7M, B8, B8M, L7, B16, 2H
Flange bolting is specified as a stud-bolt grade plus a nut grade. ASTM A193 covers high-temperature bolting (B7, B7M, B16, B8, B8M), A320 covers low-temperature bolting (L7, L7M, L43, B8 classes), A453 covers high-strength austenitic bolting (Grade 660), and A194 covers the nuts (2H, 2HM, 4, 7, 8, 8M).
What bolting & nut grades is
The "M" grades (B7M, L7M, 2HM) are hardness-limited versions for sour service under NACE MR0175 / ISO 15156. Class 1 stainless (B8 Cl.1, B8M Cl.1) is solution treated; Class 2 is strain hardened for higher strength.
- Chromium–molybdenum alloy steels (4140, 4142, 4340) quenched and tempered for B7, L7, L43
- Cr-Mo-V steel for B16 high-temperature bolting
- Austenitic stainless steel for B8 / B8M
- Precipitation-hardened iron–nickel alloy (A-286) for A453 660
Key properties
| B7 / L7 yield, min (≤ 2½ in) | 725 MPa |
|---|---|
| B7M / L7M yield, min | 550 MPa, 235 HBW max |
| B8 / B8M Cl.1 yield, min | 205 MPa |
| Common nut pairs | B7 + 2H, B7M + 2HM, L7 + 4 or 7, B8M + 8M |
| Coatings | Zinc, hot-dip galvanised, PTFE/xylan, zinc–nickel |
Bolting & nut grades grades compared
Chemistry and minimum room-temperature properties from the governing ASTM / ASME / API specifications. Open any grade for its full data sheet and PDF.
| Grade | Form | UNS | Cr% | Ni% | Mo% | C% | YieldMPa min | TensileMPa min |
|---|---|---|---|---|---|---|---|---|
| ASTM A193 B7 | Stud bolts / bolting | G41400 | 0.75–1.20 | — | 0.15–0.25 | 0.37–0.49 | 720 | 860 |
| ASTM A193 B7M | Stud bolts / bolting | G41400 | 0.75–1.20 | — | 0.15–0.25 | 0.37–0.49 | 550 | 690 |
| ASTM A193 B16 | Stud bolts / bolting | K14072 | 0.80–1.15 | — | 0.50–0.65 | 0.36–0.47 | 725 | 860 |
| ASTM A193 B8 Cl.1 | Stud bolts / bolting | S30400 | 18.0–20.0 | 8.0–11.0 | — | 0.08 max | 205 | 515 |
| ASTM A193 B8M Cl.1 | Stud bolts / bolting | S31600 | 16.0–18.0 | 10.0–14.0 | 2.00–3.00 | 0.08 max | 205 | 515 |
| ASTM A320 L7 | Stud bolts / bolting | G41400 | 0.80–1.10 | — | 0.15–0.25 | 0.38–0.48 | 725 | 860 |
| ASTM A194 2H | Heavy hex nuts | — | — | — | — | 0.40 min | — | proof 1205 |
| ASTM A194 2HM | Heavy hex nuts | — | — | — | — | 0.40 min | — | proof 1035 |
| ASTM A194 8 | Heavy hex nuts | S30400 | 18.0–20.0 | 8.0–11.0 | — | 0.08 max | — | proof 550 |
| ASTM A194 8M | Heavy hex nuts | S31600 | 16.0–18.0 | 10.0–14.0 | 2.00–3.00 | 0.08 max | — | proof 550 |
| ASTM A320 L7M | Stud bolts / bolting | G41400 | 0.80–1.10 | — | 0.15–0.25 | 0.38–0.48 | 550 | 690 |
| ASTM A320 L43 | Stud bolts / bolting | G43400 | 0.70–0.90 | 1.65–2.00 | 0.20–0.30 | 0.38–0.43 | 725 | 860 |
| ASTM A453 Grade 660 Cl.A | High-temperature bolting | S66286 | 13.5–16.0 | 24.0–27.0 | 1.00–1.50 | 0.08 max | 585 | 895 |
| ASTM A194 Grade 7 | Heavy hex nuts | G41400 | 0.75–1.20 | — | 0.15–0.25 | 0.37–0.49 | — | proof 1205 |
Reference information compiled from the published standard for convenience. It does not replace the current edition of the governing standard, which takes precedence. Verify critical dimensions and properties before design, purchase or fabrication. Teshi Engineers & Sales Promoters (P) Ltd accepts no liability for errors or omissions.
Specifications by product form
| Product form | Grades |
|---|---|
| Stud bolts / bolting | ASTM A193 B7, ASTM A193 B7M, ASTM A193 B16, ASTM A193 B8 Cl.1, ASTM A193 B8M Cl.1, ASTM A320 L7, ASTM A320 L7M, ASTM A320 L43 |
| Heavy hex nuts | ASTM A194 2H, ASTM A194 2HM, ASTM A194 8, ASTM A194 8M, ASTM A194 Grade 7 |
| High-temperature bolting | ASTM A453 Grade 660 Cl.A |
Where bolting & nut grades is used
- Flange bolting for process piping
- Pressure vessel and heat exchanger closures
- Valve body bolting
- Low-temperature and cryogenic service (L7, L43, B8 Cl.1)
- Sour oil and gas service (B7M, L7M, 2HM)
Welding and fabrication
Stud bolts are supplied with full-length threads to ASME B1.1 (8-UN for 1 in and above) and lengths to ASME B16.5 tables. Specify coating, tightening method and whether impact testing (A320) is required. Teshi manufactures stud bolts and nuts as an OEM.
FAQ
Bolting & nut grades: common questions
What nut goes with a B7 stud bolt?
ASTM A194 Grade 2H heavy hex nuts. For B7M studs in sour service use 2HM nuts.
What is the difference between B7 and B7M?
Same steel; B7M is tempered to a maximum hardness of 235 HBW (22 HRC) for sour service, so its minimum yield is 550 MPa instead of 725 MPa.
Which bolting is used for low temperature?
ASTM A320 L7 (impact-tested at −101 °C) with A194 Grade 4 or 7 nuts; L7M for sour low-temperature service.
Bolting products from Teshi Group
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