A194

Scope

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

2H

2HM

4

7

7M

8

8M

Carbon steel heavy hex nuts

Quenched & tempered carbon steel heavy hex nuts

Quenched & tempered carbon steel heavy hex nuts

Quenched & tempered carbon-molybdenum heavy hex nuts

Quenched & tempered alloy steel heavy hex nuts

Quenched & tempered alloy steel heavy hex nuts

Stainless AISI 304 heavy hex nuts

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

ASTM A194 Grade 2

Medium Carbon Steel

1/4 – 4

0

150

159

352

1,2,3

ASTM A194 Grade 2H

Medium Carbon Steel, Quenched and Tempered

1/4 – 4

850

175

C24

C38

1,2

ASTM A194 Grade 2HM

Medium Carbon Steel, Quenched and Tempered

1/4 – 4

1150

150

159

237

1,2,3

ASTM A194 Grade 4

Medium Carbon Alloy Steel, Quenched and Tempered

1/4 – 4

1100

175

C24

C38

1,2

ASTM A194 Grade 7

Medium Carbon Alloy Steel, Quenched and Tempered

1/4 – 4

1100

175

C24

C38

1,2

ASTM A194 Grade 7M

Medium Carbon Alloy Steel, Quenched and Tempered

1/4 – 4

1150

150

159

237

1,2,3

ASTM A194 Grade 8

Stainless AISI 304

1/4 – 4

-

80

126

300

4

ASTM A194 Grade 8M

Stainless AISI 316

1/4 – 4

-

80

126

300

4

NOTES:

  • 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.

  • Properties shown are those of coarse and 8-pitch thread heavy hex nuts.

  • Hardness numbers are Brinell Hardness.

  • Nuts that are carbide-solution treated require additional letter A – 8A or 8MA.

  • 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. Nuts coated with zinc have an asterisk (*) marked after the grade symbol. Nuts coated with cadmium shall have a plus sign (+) marked after the grade symbol.

  • 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%