ASTM A194 Grade 2H
The standard heavy hex nut for A193 B7 studs — quenched and tempered carbon steel, 175 ksi proof load, 24 to 35 HRC.
What A194 2H is.
ASTM A194 Grade 2H is the heavy hex nut that goes on almost every A193 B7 stud bolt. It is a medium-carbon steel with at least 0.40 percent carbon, quenched and tempered to 248 to 327 HBW in sizes up to 1½ in., and proof-load rated at 175 ksi so the nut always outlasts the stud in tension.
2H is a heavy hex pattern by default: across-flats and thickness are larger than a finished hex nut of the same thread, which is what gives the flange joint its bearing area. We machine 2H nuts from certified bar in imperial and metric threads, plain or coated, with oversize tapping for PTFE-coated studs.
Chemical composition.
| Element | Symbol | Min % | Max % |
|---|---|---|---|
| Carbon | C | 0.40 | — |
| Manganese | Mn | — | 1.00 |
| Phosphorus | P | — | 0.040 |
| Sulfur | S | — | 0.050 |
| Silicon | Si | — | 0.40 |
Values per ASTM A194/A194M-24, Tables 1, 2 and 5 (verified against the specification). Confirm the edition called out on your purchase order with our estimating team.
Mechanical properties.
| Nut style and size (in.) | Proof load stress (ksi) | Hardness, min | Hardness, max |
|---|---|---|---|
| Heavy hex, 1½ and under | 175 | 248 HBW / 24 HRC | 327 HBW / 35 HRC |
| Heavy hex, over 1½ | 175 | 212 HBW / 95 HRB | 327 HBW / 35 HRC |
| Hex (finished pattern), 1½ and under | 150 | 248 HBW / 24 HRC | 327 HBW / 35 HRC |
| Hex (finished pattern), over 1½ | 150 | 212 HBW / 95 HRB | 327 HBW / 35 HRC |
Values per ASTM A194/A194M-24, Tables 1, 2 and 5 (verified against the specification). Confirm the edition called out on your purchase order with our estimating team.
Specifications that apply.
How A194 2H ships from Houston.
- Heavy hex nuts (the default for pressure bolting)
- Finished hex nuts
- Jam nuts
- Custom and special nuts to drawing
A194 2H fasteners we make.
Every item is manufactured to your drawing or standard in A194 2H, imperial or metric, with an EN 10204 3.1 certificate.
What is ASTM A194 2H?
ASTM A194 covers nuts for high-pressure and high-temperature bolting, and Grade 2H is its quenched-and-tempered carbon steel member. The H indicates a heat-treated nut (A194 Table 7), and 2H is proof-rated for both hex and heavy hex patterns: the grade is defined for heavy hex nuts, and the specification requires them to be heat treated to a hardness of 24 to 35 HRC in sizes up to 1½ in. (a 95 HRB minimum applies above that, because a large nut cannot be through-hardened as uniformly). The proof load stress of 175 ksi for heavy hex nuts (150 ksi for the finished hex pattern) applies at every size — the proof load in pounds simply scales with the thread stress area — and comfortably exceeds the 125 ksi tensile strength of a B7 stud, which is the design intent — a joint should fail by stud fracture, never by thread stripping in the nut.
2H versus 2HM, 7 and 4
- 2HM: the same nut tempered to 235 HBW maximum for NACE sour service; pairs with B7M and L7M studs.
- Grade 7: chromium-molybdenum (4140) nut for elevated temperature; pairs with B7, B16 and L7.
- Grade 4: a carbon-molybdenum nut withdrawn from current editions of A194, found only on legacy drawings; Grade 7 replaces it.
- Grade 2: the non-heat-treated carbon steel nut with a 150 ksi proof load; rarely used with alloy studs.
Coatings and oversize tapping
When studs are PTFE coated or hot-dip galvanized, the nut is tapped oversize so the assembly still runs freely. A194 itself sets threads to ASME B1.1 and warns that modified thread dimensions can reduce load-carrying ability, so the overtap follows the coating specification and the nut is proof tested after tapping. Tell us the stud coating when you order and we tap to suit.
Proof load and nut size
A194 sets proof load as a stress, so the 175 ksi figure for a heavy hex 2H nut is the same whether the nut is ¼ inch or 4 inches. What changes is the proof load in pounds, which is the stress multiplied by the thread stress area of the mating bolt: about 24,800 lbf for a ½-13 heavy hex nut and 261,000 lbf for 1½-8. A finished-pattern (non-heavy) hex nut in Grade 2H is rated at 150 ksi because its thinner section engages fewer threads. Proof load tests follow Table 3 to 1½ inch and Supplementary Requirement S4 above that; nuts not proof tested are qualified by cross-sectional hardness.
Testing, certification and marking
- Hardness tested per lot; proof-load tested on request or where the specification requires it
- Grade symbol 2H, or 2HB on nuts machined from bar (ASTM A194 Table 7), and manufacturer's identification on one face of every nut
- EN 10204 3.1 material test report with heat number and chemistry; 3.2 witness available
- Oversize tapping for coated studs and PTFE / zinc / hot-dip galvanized finishes available
Recent A194 2H jobs.
ASTM A193 Grade B7
The workhorse alloy-steel bolting grade for flanges, valves and pressure equipment — 125 ksi tensile, quenched and tempered 4140.
ASTM A194 / ASME SA-194ASTM A194 Grade 2HM
The sour-service heavy hex nut — 2H tempered to 235 HBW max for NACE MR0175, matched to A193 B7M and A320 L7M studs.
ASTM A194 / ASME SA-194ASTM A194 Grade 7
The Cr-Mo heavy hex nut — same 4140 steel as a B7 stud, rated for elevated temperature and the usual match for B16 and L7.