ASTM A194 Grade 43
The 4340 heavy hex nut — the deep-hardening companion to A320 L43 studs and an alternative to Grade 7 on large low-temperature joints.
What A194 43 is.
ASTM A194 Grade 43 is a quenched-and-tempered nut in AISI 4340, the same nickel-chromium-molybdenum steel as A320 L43 studs. It shares the 175 ksi proof stress and 24 to 35 HRC hardness window of Grades 2H, 3, 7 and 16, and its nickel content lets large nuts harden through uniformly.
Grade 43 is normally ordered impact tested (Grade 43L) with L43 studs for cryogenic and cold-climate flanges. We machine it to order from certified 4340 bar.
Chemical composition.
| Element | Symbol | Min % | Max % |
|---|---|---|---|
| Carbon | C | 0.38 | 0.43 |
| Manganese | Mn | 0.60 | 0.85 |
| Phosphorus | P | — | 0.035 |
| Sulfur | S | — | 0.040 |
| Silicon | Si | 0.15 | 0.35 |
| Nickel | Ni | 1.65 | 2.00 |
| Chromium | Cr | 0.70 | 0.90 |
| Molybdenum | Mo | 0.20 | 0.30 |
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, all sizes | 175 | 248 HBW / 24 HRC | 327 HBW / 35 HRC |
| Hex (finished pattern), all sizes | 150 | 248 HBW / 24 HRC | 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 43 ships from Houston.
- Heavy hex nuts
- Finished hex nuts
- Custom nuts to drawing
A194 43 fasteners we make.
Every item is manufactured to your drawing or standard in A194 43, imperial or metric, with an EN 10204 3.1 certificate.
What is ASTM A194 Grade 43?
Grade 43 was added to A194 so that the 4340 steel of A320 L43 studs could be matched with a nut of the same analysis. Quenched and tempered at 1100 °F minimum, it meets the same 175 ksi proof stress and 248 to 327 HBW window as Grade 7, but its 1.65 to 2.00 percent nickel gives it the through-hardening needed for large heavy hex nuts. When impact tested to A320 it is marked 43L (43LB when machined from bar).
Testing, certification and marking
- Hardness and proof-load tested per lot on the finished product
- Grade or alloy marking 43 (43L when impact tested) and manufacturer's identification on every piece
- EN 10204 3.1 material test report with heat number and chemistry; 3.2 witness available
ASTM A320 Grade L43
4340 low-temperature bolting — L7 strength in diameters up to 4 in., thanks to the deep hardenability of a nickel-chrome-moly steel.
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.
ASTM A194 / ASME SA-194ASTM 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.