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ASTM A194

The ASTM A194 specification covers carbon, alloy, and stainless steel nuts intended for use in high-pressure and/or high-temperature service. Unless otherwise specified, the American National Standard Heavy Hex Series (ANSI B 18.2.2) shall be used. Nuts up to and including 1-inch nominal size shall be UNC Series Class 2B fit. Nuts over 1-inch nominal size shall be either UNC Series Class 2B fit or 8 UN Series Class 2B fit. High strength ASTM A194 grade 2H nuts are common in the marketplace and are often substituted for ASTM A563 grade DH nuts due to the limited availability of DH nuts in certain diameters and finishes.

A194 Grades

2 Carbon steel heavy hex nuts
2H Quenched & tempered carbon steel heavy hex nuts
2HM Quenched & tempered carbon steel heavy hex nuts, 100% hardness tested
4 Quenched & tempered carbon-molybdenum heavy hex nuts (withdrawn in 2017)
7 Quenched & tempered alloy steel heavy hex nuts
7M Quenched & tempered alloy steel heavy hex nuts, 100% hardness tested
7L Quenched & tempered alloy steel heavy hex nuts, Charpy impact tested
8 Stainless AISI 304 heavy hex nuts
8M Stainless AISI 316 heavy hex nuts

A194 Mechanical Properties

Grade Identification Marking5 Specification Material Nominal Size, In. Tempering Temp. °F Proof Load Stress, ksi Hardness Rockwell See Note
Min Max
2 ASTM A194 Grade 2 Medium Carbon Steel 1/4 - 4 0 150 159 352 1,2,3
2H ASTM A194 Grade 2H Medium Carbon Steel, Quenched and Tempered 1/4 - 4 850 175 C24 C38 1,2
2HM ASTM A194 Grade 2HM Medium Carbon Steel, Quenched and Tempered 1/4 - 4 1150 150 159 237 1,2,3
4 ASTM A194 Grade 4 Medium Carbon Alloy Steel, Quenched and Tempered 1/4 - 4 1100 175 C24 C38 1,2
7 ASTM A194 Grade 7 Medium Carbon Alloy Steel, Quenched and Tempered 1/4 - 4 1100 175 C24 C38 1,2
7M ASTM A194 Grade 7M Medium Carbon Alloy Steel, Quenched and Tempered 1/4 - 4 1150 150 159 237 1,2,3
8 ASTM A194 Grade 8 Stainless AISI 304 1/4 - 4 - 80 126 300 4
8M ASTM A194 Grade 8M Stainless AISI 316 1/4 - 4 - 80 126 300 4
NOTES:
  1. The markings shown for all grades of A194 nuts are for cold formed and hot forged nuts. When nuts are machined from bar stock, the nut must additionally be marked with the letter 'B'. The letters H and M indicate heat treated nuts.
  2. Properties shown are those of coarse and 8-pitch thread heavy hex nuts.
  3. Hardness numbers are Brinell Hardness.
  4. Nuts that are carbide-solution treated require additional letter A - 8A or 8MA.
  5. All nuts shall bear the manufacturer’s identification mark. Nuts shall be legibly marked on one face to indicate the grade and process of the manufacturer. Marking of wrench flats or bearing surfaces is not permitted unless agreed upon between manufacturer and purchaser.
  6. Other less common grades exist, but are not listed here.
Inch Fastener Standards. 7th ed. Cleveland: Industrial Fasteners Institute, 2003. N-80 - N-81.

A194 Chemical Properties

Element 2, 2H, and 2HM 4 7 and 7M (AISI 4140) 8 (AISI 304) 8M (AISI 316)
Carbon 0.40% min 0.40 - 0.50% 0.37 - 0.49% 0.08% max 0.08% max
Manganese 1.00% max 0.70 - 0.90% 0.65 - 1.10% 2.00% max 2.00% max
Phosphorus, max 0.040% 0.035% 0.035% 0.045% 0.045%
Sulfur, max 0.050% 0.040% 0.040% 0.030% 0.030%
Silicon 0.40% max 0.15 - 0.35% 0.15 - 0.35% 1.00% max 1.00% max
Chromium 0.75 - 1.20% 18.0 - 20.0% 16.0 - 18.0%
Nickel 8.0 - 11.0% 10.0 - 14.0%
Molybdenum 0.20 - 0.30% 0.15 - 0.25% 2.00 - 3.00%