Bolt Grades Explained: A325 vs B7 vs 2H — What’s the Difference?
Grade markings on a bolt head look like a small detail, but they carry real engineering meaning — material, heat treatment, and tensile strength are all encoded in that stamp. Mixing up A325, B7, and 2H isn’t just a paperwork error; it can mean the wrong bolt in a connection it was never rated for.
Here’s what each one actually specifies, and where each belongs.
What These Grades Actually Are
| Grade | What It Specifies |
|---|---|
| ASTM A325 | High-strength structural bolt standard — heavy hex bolts specifically for steel-to-steel structural connections |
| ASTM A193 B7 | Alloy steel bolting standard for high-temperature and high-pressure service — chromium-molybdenum steel, quenched and tempered |
| ASTM A194 Grade 2H | Heavy hex nut standard designed to match B7 studs/bolts — carbon steel, quenched and tempered |
ASTM A325 — Structural Steel Connections
A325 is the standard most engineers reach for when connecting structural steel members — beam-to-column, splice plates, base connections. It’s manufactured as a heavy hex bolt, rated for high clamping force, and is the default specification on most structural steel drawings across India and internationally.
Use it for: steel structure connections, structural steel fabrication, any application where the drawing calls out a structural bolt grade explicitly.
ASTM A193 B7 — High-Temperature, High-Pressure Service
B7 is a different category of application entirely. It’s an alloy steel bolt grade built for pressure vessels, piping flanges, valves, and equipment operating at elevated temperature and pressure — refineries, power plants, process industries. The chromium-molybdenum alloy and quench-and-temper treatment give it the strength retention that plain structural steel can’t match at high temperatures.
Use it for: flange connections, pressure vessel bolting, piping systems, any high-temperature or high-pressure industrial service.
ASTM A194 Grade 2H — The Nut That Matches B7
2H isn’t a bolt grade at all — it’s a heavy hex nut grade, specifically designed to be used with B7 studs and bolts. Using a mismatched nut grade with a B7 stud undermines the entire connection’s rated strength, so 2H nuts are effectively mandatory wherever B7 is specified.
Use it for: pairing with B7 studs and bolts — always match grade for grade in pressure and high-temperature applications.
How to Tell Them Apart on Site
- Check the head marking — A325, B7, and 2H are typically stamped directly on the bolt head or nut face
- A325 bolts are heavy hex, structural-profile — used in steel frame connections
- B7 studs are usually fully threaded rod-style, paired with 2H nuts at both ends in flange assemblies
- If the drawing specifies a pressure or temperature rating, you’re in B7/2H territory, not A325
Getting the Grade Right the First Time
Bharat Industrial Supplier stocks ASTM Bolt, Structural Bolt & Nuts, and 2H Nut (Heavy Hex) with full material test certificates for traceability. If your project spec references a grade you’re not certain about, send us the drawing callout and we’ll confirm exactly what you need before you order.