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ASTM 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.
Grades
2
Carbon steel heavy hex nuts
2H
Quenched & tempered carbon steel heavy hex nuts
2HM
Quenched & tempered carbon steel heavy hex nuts
4
Quenched & tempered carbon-molybdenum heavy hex nuts
7
Quenched & tempered alloy steel heavy hex nuts
7M
Quenched & tempered alloy steel heavy hex nuts
8
Stainless AISI 304 heavy hex nuts
8M
Stainless AISI 316 heavy hex nuts
Mechanical Properties
Grade Identification Markings
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
1000
150
159
352
1,2,3
ASTM A194 Grade 2H
Medium Carbon Steel, Quenched and Tempered
1/4 - 4
1000
175
C24
C38
1,2
ASTM A194 Grade 2HM
Medium Carbon Steel, Quenched and Tempered
1/4 - 4
1000
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
1100
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:
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. 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.
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.
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