In the article about Property Class as per ASME (The American Society of Mechanical Engineers) we have seen that there are many ASME specifications for making threaded fasteners. In this article information is given about their scope. Grades of material available in each specification are also listed. Specifications contain information on ordering, manufacturing process, heat treatment, chemical composition, mechanical requirements, etc. Information is also given on supplementary requirement to be specified in purchase order. For detail information, please refer the specifications.
Note:
This article is theoretical in nature and is given to maintain sequence of articles on threaded fasteners. You may skip reading this article or read underlined key words.
Terminology
Bolting material – Rolled or forged bars or blanks, wire, rod, threaded bar, rotary pierced or extruded seamless tubes, bored bars, or forged hollows from forged or rolled bar segments to be manufactured into bolts, screws, studs, washers, and nuts.
Grade – An alloy described individually and identified by its own designation in a table of chemical requirements within any specification.
Class – A term used to differentiate between different heat treatment conditions or strength levels, or both, often within the same Grade but sometimes within the same family of materials. May also apply to work hardened condition or strength level, or both.
ASME Specification SA–962 / SA–962M
SA 962 / SA 962M is – Specification for common requirements for steel fasteners or fastener materials, or both, intended for use at any temperature from cryogenic to the creep range. Its scope covers a group of common requirements that shall apply to carbon, alloy and stainless steel fasteners or fastener materials, or both under any of the following ASTM (The American Society for Testing and Materials) specification numbers.
A 193 / A 193M
A 194 / A 194M
A 320 / A 320M
A 437 / A 437M
A 453 / A 453M and
A 540 / A 540M
As per the supplementary requirements, bolts, studs and bolting material for dynamic service shall be examined for decarburization and surface discontinuities as under.
The surface discontinuities shall conform to specification ASTM F 788 / 788M.
Thread lap inspection shall be performed in accordance with ASTM F 788 / 788M. Threads shall have no laps at the root, or on the flanks initiating or extending below the pitch line.
Quench cracks of any depth, any length, or in any location are not permitted.
Folds at the junction of the head and the shank are not permitted.
A stress relieving operation shall follow straightening or cold drawing (for dimensional control) after heat treatment.
Note:
When ASTM material is shown under ASME number, S is added in front of ASTM number. For example, specification A 193 of ASTM is called SA-193 under ASME.
ASME Specification SA–193 / SA–193M
ASME SA 193 / SA 193M is – Specification for alloy-steel and stainless steel bolting material for high-temperature service. Its scope covers alloy and stainless steel bolting material for pressure vessels, valves, flanges and fittings for high-temperature service.
In the specification, many grades of ferritic and austenitic steel are given as under. Selection of a grade will depend upon design, service conditions, mechanical properties and high-temperature characteristics.
| Type | Grade | Description |
|---|---|---|
| Ferritic Steel | B5 | 5 % Chromium |
| Ferritic Steel | B6, B6X | 12 % Chromium, AISI Type 410 |
| Ferritic Steel | B7, B7M | Chromium-Molybdenum |
| Ferritic Steel | B16 | Chromium-Molybdenum-Vanadium |
| Austenitic Steel | B8, B8A | AISI Type 304 |
| Austenitic Steel | B8C, B8CA | AISI Type 347 |
| Austenitic Steel | B8M, B8MA, B8M2, B8M3 | AISI Type 316 |
| Austenitic Steel | B8P, B8PA | AISI Type 305 with restricted Carbon |
| Austenitic Steel | B8N, B8NA | AISI Type 304N |
| Austenitic Steel | B8MN, B8MNA | AISI Type 316N |
| Austenitic Steel | B8MLCuN, B8MLCuNA | Unstabilized, 20 Chromium, 18 Nickel, 6 Molybdenum with restricted Carbon |
| Austenitic Steel | B8T, B8TA | AISI Type 321 |
| Austenitic Steel | B8R, B8RA | 22 Chromium-13 Nickel-5 Manganese |
| Austenitic Steel | B8S, B8SA | 28 Chromium-8 Nickel-4 Silicon + Nitrogen |
| Austenitic Steel | B8LN, B8LNA | AISI Type 304N with restricted Carbon |
| Austenitic Steel | B8MLN, B8MLNA | AISI Type 316N with restricted Carbon |
For a grade of material, there are many classes depending on heat treatment. For example, Grade B8 has three classes, Class 1, Class 2 and Class 2B.
Austenitic stainless steel may be carbide solution treated or carbide solution treated and strain hardened.
Chemical composition of some grades is as under
| ASTM A-193/ASME SA-193 | ||||||
|---|---|---|---|---|---|---|
| Grade | B5 | B6 | B7/B7M | B16 | B8 | B8M |
| C | 0.10 min | 0.15 max | 0.37-0.49 | 0.36-0.47 | 0.08 max | 0.08 max |
| Mn | 1.00 max | 1.00 max | 0.65-1.10 | 0.65-1.10 | 2.00 max | 2.00 max |
| P, max | 0.040 | 0.040 | 0.035 | 0.035 | 0.045 | 0.045 |
| S, max | 0.030 | 0.030 | 0.040 | 0.04 | 0.030 | 0.030 |
| Si | 1.00 max | 1.00 max | 0.15-0.35 | 0.15-0.35 | 1.00 max | 1.00 max |
| Ni | - | - | - | - | 8.00-10.50 | 10.00-14.00 |
| Cr | 4.00-6.00 | 11.50-13.50 | 0.75-1.20 | 0.80-1.15 | 18.00-20.00 | 16.00-18.00 |
| Mo | 0.40-0.65 | - | 0.15-0.25 | 0.50-0.65 | - | 2.00-3.00 |
| V | - | - | - | 0.25-0.35 | - | - |
| Al, max | - | - | - | 0.015 | - | - |
Note:
For grades of alloy-steel bolting material suitable for use at lower range of high-temperature applications, reference should be made to ASME Specification SA 354.
ASME Specification SA–194 / SA–194M
ASME SA 194 / SA 194M is – Specification for carbon and alloy steel nuts for bolts for high-pressure or high-temperature service, or both. Its scope covers a variety of carbon, alloy and martensitic stainless steel nuts in the size range M6 through M100 nominal. It also covers austenitic stainless steel nuts in the size range M6 nominal and above.
Nuts are made in many grades as under to suit variety of bolting material.
| Grade Symbol | Material |
|---|---|
| 1 | Carbon |
| 2, 2HM and 2H | Carbon |
| 4 | Carbon, molybdenum |
| 3 | AISI 501 |
| 6 | AISI 410 |
| 6F | AISI 416 with sulfur |
| 6F | AISI 416 with selenium |
| 7, 7M | AISI 4140 / AISI 4142 / AISI 4145 / 4140H, 4142H, 4145H |
| 8, 8A | AISI 304 |
| 8C, 8CA | AISI 347 |
| 8M, 8MA | AISI 316 |
| 8T, 8TA | AISI 321 |
| 8F, 8FA | AISI 303 with sulfur |
| 8F, 8FA | AISI 303 with selenium |
| 8P, 8PA | AISI 305 with restricted carbon |
| 8N, 8NA | AISI 304N |
| 8LN, 8LNA | AISI 304N with restricted carbon |
| 8MN, 8MNA | AISI 316N |
| 8MLN, 8MLNA | AISI 316N with restricted carbon |
| 8R, 8RA | XM19 |
| 8S, 8SA | - |
| 8MLCuN, 8MLCuNA | S31254 |
| 9C, 9CA | N08367 |
| 16 | Chromium Molybdenum vanadium |
Chemical composition of some grades is as under
| ASTM A-194/ASME SA-194 | |||||||
|---|---|---|---|---|---|---|---|
| Grade | 2H/2HM | 3 | 4 | 6 | 7/7M | 8 | 8M |
| C | 0.40 min | 0.10 min | 0.40-0.50 | 0.15 max | 0.37-0.49 | 0.08 max | 0.08 max |
| Mn | 1.00 max | 1.00 max | 0.70-0.90 | 1.00 max | 0.65-1.10 | 2.00 max | 2.00 max |
| P, max | 0.040 | 0.040 | 0.035 | 0.040 | 0.040 | 0.045 | 0.045 |
| S, max | 0.050 | 0.030 | 0.040 | 0.030 | 0.040 | 0.030 | 0.030 |
| Si | 0.40 max | 1.00 max | 0.15-0.35 | 1.00 max | 0.15-0.35 | 1.00 max | 1.00 max |
| Ni | - | - | - | - | - | 8.00-10.50 | 10.00-14.00 |
| Cr | - | 4.00-6.00 | - | 11.50-13.50 | 0.75-1.20 | 18.00-20.00 | 16.00-18.00 |
| Mo | - | 0.40-0.65 | 0.20-0.30 | - | 0.15-0.25 | - | 2.00-3.00 |
When strain hardening is required with strain hardened Grades 8, 8C, 8T, 8M, 8F, 8P, 8N or 8MN, it shall be specified in the order. For this, nuts shall be machined from cold drawn bars or shall be cold forged to shape. No subsequent heat treatment shall be performed on the nuts.
Coatings on nuts are prohibited unless specified by the purchaser. Use of coated fasteners at temperature above approximately one-half the melting point of coating is not recommended unless consideration is given to the potential for liquid and solid metal embrittlement, or both. The melting point of elemental zinc is approximately 415 ºC. Therefore, application of zinc coated fasteners should be limited to temperature less than 210ºC.
ASME Specification SA–307
ASME SA 307 is – Specification for carbon steel bolts and studs, 60000 PSI tensile strength. Its scope covers the chemical and mechanical requirements of three grades of carbon steel bolts and studs in sizes ¼ inch through 4 inch. The fasteners are designated by “Grade†denoting tensile strength and intended use as follows.
| Grade | Description |
|---|---|
| Grade A | Bolts and studs having a minimum tensile strength of 60 ksi (414 MPa) and intended for general applications. |
| Grade B | Bolts and studs having a tensile strength of 60 to 100 ksi (414 to 690 MPa) and intended for flanged joints in piping system with cast iron flanges. |
| Grade C | Nonheaded anchor bolts (studs), either bent or straight, having properties conforming to Specification A 36 (tensile strength of 58 to 80 ksi – 400 to 550 MPa) and intended for structural anchorage purposes. |
Suitable nuts are covered in specification SA 563. Unless otherwise specified, the grades shall be as follows.
| Fastener Grade and Size | Nut Grade and Style |
|---|---|
| A, C, ¼ to 1 ½ inch | A, hex |
| A, C, over 1 ½ to 4 inch | A, heavy hex |
| B, ¼ to 4 inch | A, heavy hex |
Supplementary requirement shall be included in the purchase order if bolts are to be welded.
ASME Specification SA–320 / SA-320M
SA 320 / SA 320M is – Specification for alloy steel bolting material for low-temperature service. Its scope covers alloy steel bolting materials for pressure vessels, valves, flanges and fittings for low-temperature service. Its scope covers several grades, including both ferritic and austenitic steels as under.
| Type | Identification Symbol | Grade |
|---|---|---|
| Ferritic Steels | L7, L7M, L70 | Chromium-Molybdenum (AISI 4140,4142, or 4145) |
| Ferritic Steels | L7A, L71 | Carbon-Molybdenum (AISI 4037) |
| Ferritic Steels | L7B, L72 | Chromium-Molybdenum (AISI 4137) |
| Ferritic Steels | L7C, L73 | Nickle-Chromium-Molybdenum (AISI 8740) |
| Ferritic Steels | L43 | Nickle-Chromium-Molybdenum (AISI 4340) |
| Ferritic Steels | L1 | Low-Carbon Boron |
| Austenitic Steels | B8, B8A | Unstabilized 18 Chromium-8 Nickel (AISI Type 304) |
| Austenitic Steels | B8C, B8CA | Stabilized 18 Chromium-8 Nickel (AISI Type 347) |
| Austenitic Steels | B8T, B8TA | Stabilized 18 Chromium-8 Nickel (AISI Type 321) |
| Austenitic Steels | B8P, B8PA | Unstabilized 18 Chromium-8 Nickel (AISI Type 305 with restricted carbon) |
| Austenitic Steels | B8F, B8FA | With added sulfur (Type 303) |
| Austenitic Steels | B8F, B8FA | With added selenium (Type 303 Se) |
| Austenitic Steels | B8M, B8MA | 18 Chromium-10 Nickel-2 Molybdenum (AISI Type 316) |
| Austenitic Steels | B8LN, B8LNA | Unstabilized 18 Chromium-8 Nickel with Nitrogen (AISI Type 304N with restricted carbon) |
| Austenitic Steels | B8MLN, B8MLNA | Unstabilized 18 Chromium-10 Nickel-2 Molybdenum with Nitrogen (AISI Type 316N with restricted carbon) |
The standard stipulates the requirements for Charpy impact energy absorption.
Nuts for use with this bolting material are covered in Section 9 of the standard and require that the nut material shall be impact tested.
Washers for use with ferritic steel bolting shall conform to Specification F 436 and with austenitic steel shall be made of austenitic steel.
ASME Specification SA–325
SA 325 is – Specification for structural bolts, steel, heat treated, 120 / 105 ksi minimum tensile strength. Its scope covers two types of quenched and tempered steel structural bolts having a minimum tensile strength of 120 ksi for sizes 1.0 inch and less and 105 ksi for sizes over 1.0 to 1 ½ inch inclusive.
The bolts are intended for use in structural connections. These connections are covered under the requirements of the Specifications for Structural Joints Using ASTM A 325 or A 490 Bolts, approved by the Research Council on Structural Connections of the Engineering Foundation.
The bolts are designated by Type denoting chemical composition as follows.
| Type | Description |
|---|---|
| Type 1 | Medium carbon, carbon boron, or medium carbon alloy steel. |
| Type 2 | Withdrawn in November 1991. |
| Type 3 | Weathering steel. |
Note:
Bolts for general application, including anchor bolts, are covered by Specification A 449. Also refer to Specification A 449 for quenched and tempered steel bolts and studs with diameters greater than 1 ½ inch but with similar mechanical properties.
Unless otherwise specified, all nuts used on these bolts shall conform to the requirements of Specification A 194 / A 194M or A 563, shall be heavy hex, as follows.
| Bolt Type and Finish | Nut Class and Finish |
|---|---|
| Type 1, Plain (uncoated) | A 563 – C, C3, D, DH, DH3, plain A 194 – 2, 2H, plain |
| Type 1, zinc-coated | A 563 – DH, zinc coated A 194 – 2, 2H, zinc coated |
| Type 3, plain | A 563 – C3, DH3, plain |
Unless otherwise specified, all washers used on these bolts shall conform to the requirements of Specification F 43 or F 959.
ASME Specification SA–354
SA 354 is – Specification for quenched and tempered alloy steel bolts, studs, and other externally threaded fasteners. Its scope covers fasteners 4 inch and under in diameter for application at normal atmospheric temperature, where high strength is required and for limited application at elevated temperature.
Two levels of bolting strength are covered, designated Grades BC and BD. Selection will depend upon design and stresses and service for which the product is to be used.
Nuts are covered in Specification A 563.
Unless otherwise specified, the grade and style of nut for each grade of fastener shall be as follows.
| Grade of Fastener and Surface Finish | Nut Grade and Style |
|---|---|
| BC plain (or with a coating of insufficient thickness to require over-tapped nuts) | C heavy hex |
| BC zinc-coated (or with a coating thickness requiring over-tapped nuts) | DH heavy hex |
| BD, all finishes | DH heavy hex |
ASME Specification SA–437 / SA-437M
SA 437 / SA 437M is – Specification for alloy-steel turbine-type bolting material specially heat treated for high-temperature service. Its scope covers material for high-temperature service such as steam turbine, gas turbine, and similar uses. This material requires special processing and should not be used for general purpose applications.
Three levels of bolting strength are covered, designated Grades B4B, B4C and B4D. Selection will depend on the design and the stresses and service for which the product is to be used.
As per the standard, all threads shall be formed after heat treatment.
ASME Specification SA–449
SA 449 is – Specification for quenched and tempered steel bolts and studs. Its scope covers two types of bolts and studs for general applications where high strength is required.
-
Type 1 – Medium-carbon steel bolts and studs furnished in nominal diameters of ¼ to 3 inch inclusive and
-
Type 2 – Low-carbon martensite or medium-carbon martensite steel bolts and studs furnished in nominal diameters of ¼ to 1 inch inclusive.
Suitable nuts are covered in Specification A 563. Unless otherwise specified, the grade and style of nut shall be as follows.
| Fastener Size and Surface Finish | Nut Grade and Style |
|---|---|
| ¼ to 1 ½ inch, plain (or with a coating of insufficient thickness to require over-tapped nuts) | B, hex |
| Over 1 ½ to 3 inch, plain (or with a coating of insufficient thickness to require over-tapped nuts) | A, heavy hex |
| ¼ to 3 inch, zinc-coated (or with a coating thickness requiring over-tapped nuts) | DH, heavy hex |
ASME Specification SA– 453 / SA-453M
SA 453 / SA 453M is – Specification for high-temperature bolting materials with expansion coefficients comparable to austenitic steels. Its scope covers four grades of bolting material. The Grades are 660, 651, 662 and 665. Their yield strength ranges from 50 to 120 ksi (345 to 827 MPa). The material is for use in high-temperature service such as fasteners for pressure vessel and valve flanges. The material requires special processing and not intended for general purpose applications.
ASME Specification SA– 540 / SA-540M
SA 540 / SA 540M is – Specification for alloy-steel bolting materials for special applications. Its scope covers regular and special-quality alloy steel bolting materials which may be used for nuclear and other special applications. Five grades of material are covered as under.
| Grade Identification Symbol | Material |
|---|---|
| B21 (Cr-Mo-V) | Chromium-Molybdenum-Vanadium |
| B22 (4142-H) | Chromium-Molybdenum |
| B23 (E-4340-H) | Chromium-Nickel-Molybdenum |
| B24 (4340 Mod.) | Chromium-Nickel-Molybdenum |
| B24V (4340V Mod.) | Chromium-Nickel-Molybdenum-Vanadium |
ASME Specification SA– 574
SA 574 is – Specification for alloy steel socket-head screws. Its scope covers requirements for quenched and tempered alloy steel hexagon socket head set screws, 0.060 through 4 inch diameter where high strength is required. The material has proof strength of 140 ksi for screw diameter of less than or equal to 0.50 inch and 135 ksi for screw diameter of 0.625 inch and larger.
The standard also gives information on amount (value) and location for permissible and nonpermissible discontinuities on socket, head and body.
ASME Specification SA– 563
SA 563 is – Specification for carbon and alloy steel nuts. Its scope covers requirements for eight grades of nuts for general structural and mechanical uses on bolts, studs and other externally threaded parts. The Grades are 0, A, B, C, D, DH, C3 and DH3. Grades C3 and DH3 have atmospheric corrosion resistance and weathering characteristics. For metric equivalents to specification A 563, please refer specification A 563M. Threads shall be formed by tapping or machining.
Recommended nuts for various bolts from Nut and Bolt Suitability Guide are as under. For information on suitable nuts, please refer Nut and Bolt Suitability Guide given in the standard.
| Grade of Bolt | Surface Finish | Nominal Size, inch | A 563 Grade and ANSI Nut style |
|---|---|---|---|
| A 307 Grade A | Non-zinc-coated and Zinc-coated | ¼ to 1 ½ | A, Hex |
| >1 ½ to 2 | A, Heavy Hex | ||
| >2 to 4 | A, Heavy Hex | ||
| A 307 Grade B | Non-zinc-coated and Zinc-coated | ¼ to 1 ½ | A, Heavy Hex |
| >1 ½ to 2 | A, Heavy Hex | ||
| >2 to 4 | A, Heavy Hex | ||
| A 325 Type 1 | Non-zinc-coated | ½ to 1 ½ | C, Heavy Hex |
| Zinc-coated | ½ to 1 ½ | DH, Heavy Hex | |
| A 325 Type 3 | Non-zinc-coated | ½ to 1 ½ | C3, Heavy Hex |
| A 354 Grade BC | Non-zinc-coated | ¼ to 1 ½ | C, Heavy Hex |
| >1 ½ to 4 | C, Heavy Hex | ||
| Zinc-coated | ¼ to 1 ½ | DH, Heavy Hex | |
| >1 ½ to 4 | DH, Heavy Hex | ||
| A 354 Grade BD | Non-zinc-coated | ¼ to 1 ½ | DH, Heavy Hex |
| >1 ½ to 4 | DH, Heavy Hex | ||
| A 394 Type 0 | Zinc-coated | ½ to 1 | A, Hex |
| A 394 Type 1 and 2 | Zinc-coated | ½ to 1 | DH, Hex |
| A 394 Type 3 | Non-zinc-coated | ½ to 1 | DH3, Hex |
| A 449 Type 1 and 2 | Non-zinc-coated | ¼ to 1 ½ | B, Hex |
| >1 ½ to 3 | A, Heavy Hex | ||
| Zinc-coated | ¼ to 1 ½ | DH, Heavy Hex | |
| >1 ½ to 3 | DH, Heavy Hex | ||
| A 490 Type 1 and 2 | Non-zinc-coated | ½ to 1 ½ | DH, Heavy Hex |
| A 490 Type 3 | Non-zinc-coated | ½ to 1 ½ | DH3, Heavy Hex |
| A 687 | Non-zinc-coated | ¼ to 3 | D, Heavy Hex |
| Zinc-coated | ¼ to 3 | DH, Heavy Hex |
ASTM A 490
This standard covers specification for two types of quenched and tempered, alloy steel, heavy hex structural bolts having a tensile strength of 150 to 173 ksi.
ASTM F 594
Standard covers specification for stainless steel nuts
ASTM F 837
Standard Specification for Stainless Steel Socket Head Cap Screws
This specification covers the chemical and mechanical requirements for stainless steel inch socket head cap screw (SHCS) with nominal thread 0.060 through 1.500 in. and intended for use in applications requiring general corrosion resistance.
ASTM F 835
Standard Specification for Alloy Steel Socket Button and Flat Countersunk Head Cap Screws
This specification covers the requirements for quenched and tempered alloy steel hexagon socket button (SBHCS) 0.060 through 0.625 thread sizes and flat countersunk (SFHCS) 0.060 through 1.5 thread sizes head cap screws having material properties for high-strength requirements. Fasteners meeting this specification are intended for shear-type applications and have tensile requirements ranging from 122 to 150 ksi.
ASTM F 879
Standard Specification for Stainless Steel Socket Button and Flat Countersunk Head Cap Screws
This specification covers the chemical and mechanical requirements for stainless steel inch hexagon socket button (SBHCS) and flat countersunk (SFHCS) head cap screws with nominal thread 0.060 through 0.625 in. intended for use in applications requiring general corrosion resistance.
ASTM F 912
Standard Specification for Alloy Steel Socket Set Screws
This specification covers the requirements for quenched and tempered alloy steel socket-set screws (SSS) 0.060 through 2.000-in. sizes having hardnesses 45 to 53 HRC.
ASTM F 880
Standard Specification for Stainless Steel Socket-Set Screws
This specification covers the requirements for austenitic grade stainless steel socket-set screws (SSS), sizes 0.060 through 0.500 in. in two conditions, AF and CW.
ASTM F 788
Standard Specification for Surface Discontinuities of Bolts, Screws, and Studs, Inch and Metric Series
This specification establishes allowable limits for the various types of surface discontinuities that may occur during the manufacture and processing of bolts, screws, and studs, including heat-treated machine screws, tapping screws, and sems (the washers of screw-washer assemblies are excluded). This specification covers metric series products with nominal diameters of 4 mm and larger and with specified minimum tensile strengths of 420 MPa and higher; and inch series products with nominal diameters of No. 5 (0.1250 in.) and larger and with specified minimum tensile strengths of 60 000 psi and higher.
When the engineering requirements of the application necessitate control of surface discontinuities on bolts, screws, or studs, the purchaser shall specify conformance to ASTM Specification F 788/F 788M, in the original inquiry and purchase order.
ASTM F 812
Standard Specification for Surface Discontinuities of Nuts, Inch and Metric Series
This specification establishes allowable limits for the various types of surface discontinuities that may occur during the manufacture and processing of metric-series nuts with nominal diameters 5 mm and larger and inch-series nuts with nominal diameters 1/4 in. and larger.
ASTM F 606
Standard Test Methods for Determining the Mechanical Properties of Externally and Internally Threaded Fasteners, Washers, Direct Tension Indicators, and Rivets
These test methods cover establishment of procedures for conducting tests to determine the mechanical properties of externally and internally threaded fasteners, washers, direct tension indicators, and rivets. Property requirements and the applicable tests for their determination are specified in individual product standards. In those instances where the testing requirements are unique or at variance with these standard procedures, the product standard shall specify the controlling testing requirements.
SAE Specification J 429
SAE stands for Society of Automotive Engineers.
SAE J 429 is – Specification for mechanical and material requirements for externally threaded fasteners. It covers the mechanical and material requirements for inch-series steel bolts, screws, studs, sems (bolts with washer), and U-bolts used in automotive and related industries in sizes to 1-1/2 in inclusive. The standard also specifies manufacturing, testing, and part identification (marking) requirements. A set of requirement is known by a grade number (e.g. 5,8, etc.). Thus a Grade refers to more than just strength level; it incorporates a comprehensive list of requirements.
