On a pressure flange, the bolting grade cannot be treated as generic hardware. Bolts used in a pressure flange should not be considered ordinary fastening hardware. The wrong selection of corrosion resistance, heat treatment and strength may render the bolt as the weak link of the connection. The specifications of ASTM A193 cover stainless steel and alloy steel bolts to be used for applications at high temperatures and high pressures as well as other special services. Manufacturer Unifit provides ASTM A193 bolts, studs and stud bolts in grades B7, B7M, B8, B8M, B16 and B6 for use in pressure vessels, valves, flanges, fittings and industrial equipment of various types. Each grade is meant to serve a certain purpose; this page provides the information that will match the grade to some conditions of service and send the buyer to the information on the detailed grade.
For the wider material and product range, see our fasteners manufacturer in India page. Always use the project specification and the applicable ASTM revision as the final basis for material selection.
Request QuoteASTM A193/A193M covers alloy-steel and stainless-steel bolting materials and bolting components used on pressure vessels, valves, flanges and fittings for high-temperature, high-pressure and other special-purpose applications. Depending on the purchase specification, the bolting may be supplied as bolts, screws, studs, stud bolts, bars or related threaded components.
The A193 designation tells the buyer the bolting material family and grade requirements; it does not replace the dimensional standard, thread specification, matching-nut requirement or project inspection plan. In many flange assemblies, ASTM A193 bolting is paired with ASTM A194 nuts, while ASTM A962/A962M provides common requirements used across several steel fastener specifications.
Related Unifit pages: industrial bolts | stud bolts | fastener standards
The correct grade is driven by the service condition rather than the grade name alone. Use the table as a routing guide, then open the linked grade page for detailed technical information.
| Grade | Material family | Typical selection logic | Hub role |
|---|---|---|---|
| ASTM A193 Grade B7 | Chromium-molybdenum alloy steel | Common high-strength bolting for refinery, petrochemical, pressure-equipment and elevated-temperature service where B7 is specified. | Primary alloy-steel grade |
| ASTM A193 Grade B7M | Modified Cr-Mo alloy steel with controlled hardness | Used where lower hardness is specified, including certain sour-service requirements subject to the governing project/NACE requirements. | Controlled-hardness option |
| ASTM A193 Grade B8 | 304-type austenitic stainless steel | Corrosion-resistant bolting where austenitic stainless steel is specified; Class 1 and Class 2 conditions address different strength/processing requirements. | Stainless / 304 family |
| ASTM A193 Grade B8M | 316-type molybdenum-bearing austenitic stainless steel | Selected when 316-type stainless chemistry and improved resistance to chloride-related corrosion are required, subject to the actual environment. | Stainless / 316 family |
| ASTM A193 Grade B16 | Chromium-molybdenum-vanadium alloy steel | High-strength bolting used for elevated-temperature service where the project specification calls for B16 rather than B7. | Elevated-temperature alloy steel |
| ASTM A193 Grade B6 | Martensitic stainless steel, commonly 410-type chemistry | Used where the specified service calls for B6 chemistry and properties, including applications requiring a chromium stainless grade. | Martensitic stainless grade |
Useful comparison guides: ASTM A193 B7 vs B8 bolts | ASTM A193 B7 vs B8 vs B8M fasteners
Grade selection begins with the joint and the operating environment. A procurement list that says only “ASTM A193 bolt” is incomplete; the grade, dimensions, thread, heat-treatment/class condition and matching components must be defined.
For austenitic grades such as B8 and B8M, the class designation is not a cosmetic suffix. Class 1 material is supplied in the applicable solution-treated condition, while Class 2 products are strain-hardened to achieve higher strength within the limits of the standard. The required class should therefore be stated in the RFQ and purchase order.
Grade-specific class pages: B8 Class 1 fasteners | B8 Class 2 fasteners | B8M Class 1 fasteners | B8M Class 2 fasteners
A193 is a bolting specification; the matching nut is commonly selected from ASTM A194 when the project requires an A193/A194 assembly. The purchase specification remains controlling, but the following combinations are widely used and provide a practical procurement check.
| A193 bolting grade | Common A194 nut grade | Procurement note |
|---|---|---|
| A193 B7 | A194 2H | Common alloy-steel high-temperature/high-pressure bolting combination. |
| A193 B7M | A194 2HM | Controlled-hardness pairing commonly used where B7M is specified. |
| A193 B8 | A194 8 | Austenitic stainless pairing; confirm class/condition and project requirements. |
| A193 B8M | A194 8M | 316-type stainless pairing; confirm service environment and project requirements. |
| A193 B6 | A194 6 | Common pairing where the B6/Grade 6 combination is specified. |
See also: ASTM A194 specification
ASTM A193 bolting is used where joint integrity must be maintained under pressure, temperature, corrosion or other demanding conditions. Typical applications include:
The inspection scope should be defined before quotation, especially for pressure-service or critical bolting. Depending on the grade and purchase specification, buyers may require verification of material identity, dimensions, hardness, mechanical properties, heat treatment, coating and traceability.
If Mill Test Certificates, EN 10204 3.1 documentation, PMI, third-party inspection or project-specific test reports are required, include them in the RFQ so the exact scope can be confirmed. Do not assume that every optional test or supplementary requirement applies unless it is stated in the purchase specification.
For a faster technical and commercial review, provide the following information with the enquiry:
| RFQ field | What to specify |
|---|---|
| A193 grade | B7, B7M, B8, B8M, B16, B6 or other specified grade. |
| Product form | Bolt, stud, stud bolt, screw or other component. |
| Class / condition | Required for applicable austenitic grades such as B8/B8M. |
| Diameter / length | Metric or imperial units; include full/partial thread requirement. |
| Thread specification | UNC, UNF, 8UN, metric or project-defined thread as applicable. |
| Dimensional standard / drawing | Applicable ASME/DIN/ISO or project drawing revision. |
| Matching nut / washer | A194 grade and washer specification where required. |
| Coating / finish | Specified coating system, thickness or finish requirement. |
| Quantity / delivery | Project quantity, delivery location and required schedule. |
| Inspection / documentation | MTC, PMI, hardness/mechanical tests, TPI or other project documents. |
ASTM A193/A193M covers alloy-steel and stainless-steel bolting materials and components for pressure vessels, valves, flanges and fittings in high-temperature, high-pressure and other special-purpose service. The exact grade must still be selected according to the design and operating conditions.
Both are chromium-molybdenum alloy-steel grades, but B7M is supplied with tighter hardness control and is commonly specified for certain sour-service requirements. The project specification, hardness limits and applicable service requirements should determine whether B7 or B7M is correct.
B8 is based on 304-type austenitic stainless steel, while B8M is based on 316-type stainless steel with molybdenum. B8M is often considered where improved resistance to chloride-related corrosion is required, but actual selection must reflect the process environment and project specification.
B16 is a chromium-molybdenum-vanadium alloy-steel bolting grade used for elevated-temperature, high-strength service where the project specification calls for B16. It should not be substituted for B7 solely on the assumption that one grade is “better”; the design requirement controls the choice.
For applicable austenitic grades such as B8 and B8M, Class 1 is supplied in the specified solution-treated condition, while Class 2 is strain-hardened for higher strength. The required class affects mechanical properties and must be stated in the purchase order.
ASTM A193 B7 is commonly paired with ASTM A194 Grade 2H nuts, while B8M is commonly paired with A194 Grade 8M. Other pairings may apply depending on the grade, class, temperature, coating and project specification, so the assembly should be checked as a system.
No. ASTM A193 is primarily associated with high-temperature, high-pressure and special-purpose bolting, while ASTM A320 covers alloy-steel and stainless-steel bolting for low-temperature service. L7 and L7M requirements should therefore be treated within the A320 specification family.
Send the A193 grade, product form, class where applicable, diameter, length, thread, dimensional standard or drawing, matching nut/washer requirement, coating or finish, quantity, delivery location and any testing or documentation requirement. This avoids unnecessary clarification before quotation.
Send your ASTM A193 grade, product type, dimensions, thread, class/condition, quantity and documentation requirements. For drawing-based or project-specific bolting, attach the latest specification or drawing revision so the requirement can be reviewed before quotation.
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