ASTM A194 Grade 7M is a standard material specification for high tensile nuts and other internally threaded fasteners, made from chromium molybdenum alloy steel. Grade 7M nuts can be produced by means of hot forging, cold forging or machining from bar stock (Grade Type AISI 4140/4142/4145/4140H/4142H/4145H) followed by heat treatment. ASTM A194 specification covers requirements for chemical composition, heat treatment, hardness, proof load, etc., for Grade 7M nuts.
Element |
Alloy Steel |
|---|---|
| Chromium Molybdenum Steel | |
| CompositionA, % | |
| Carbon | 0.37 - 0.49 |
| Manganese | 0.65 - 1.10 |
| Phosphorus | 0.035 max |
| Sulfur | 0.04 max |
| Silicon | 0.15 - 0.35 |
| Chromium | 0.75 - 1.20 |
| Molybdenum | 0.15 - 0.25 |
AThe intentional addition of Bi, Se, Te, and Pb is not permitted.
| Grade | Completed Nuts | Sample Nut After Heat Treatment | |||
|---|---|---|---|---|---|
| Brinell Hardness, BHN |
Rockwell Hardness | Brinell Hardness, BHN, min |
Rockwell Hardness, HRB, min |
||
| HRC | HRB | ||||
| 7M | 159 - 235 | ... | 84 - 99 | 159 | 84 |
Heat Treatment: Grade 7M shall be quenched and tempered at a temperature of at least 1150 °F [620 °C].
| Nominal Size, Inch. | Threads Per Inch | Proof Load, lbf | |
|---|---|---|---|
| Heavy HexA | HexB | ||
| 1/4 | 20 | 4 770 | 4 300 |
| 5/16 | 18 | 7 860 | 7 070 |
| 3/8 | 16 | 11 620 | 10 460 |
| 7/16 | 14 | 15 940 | 14 350 |
| 1/2 | 13 | 21 280 | 19 160 |
| 9/16 | 12 | 27 300 | 24 570 |
| 5/8 | 11 | 33 900 | 30 510 |
| 3/4 | 10 | 50 100 | 45 090 |
| 7/8 | 09 | 69 300 | 62 370 |
| 01 | 08 | 90 900 | 81 810 |
| 1-1/8 | 08 | 118 500 | 106 700 |
| 1-1/4 | 08 | 150 000 | 135 000 |
| 1-3/8 | 08 | 185 000 | 166 500 |
| 1-1/2 | 08 | 223 800 | 201 400 |
A: Based on proof stress of 150 000 psi.
B: Based on proof stress of 135 000 psi.
| Commonly Produced Grade 7M Nuts | ||||
|---|---|---|---|---|
| Hex Nuts | Heavy Hex Nuts | Jam Nuts | Heavy Hex Jam Nuts | Castle Nuts |
| Coupling Nuts | Square Nuts | Thin Square Nuts | All Metal Lock Nuts | Dome Nuts |